Video Encoder, a Video Decoder and Corresponding Methods of Processing MMVD Distance

ABSTRACT

A method of determining a distance table of a merge with motion vector difference (MMVD) mode, wherein the method comprises determining a reference picture from at least one reference picture list of a current processing unit based on at least one parameter of the reference picture, and obtaining the distance table for the current processing unit based on the reference picture, wherein the at least one parameter of the reference picture comprises a picture order count (POC) number of the reference picture, a number of MMVD blocks of the reference picture, a reference picture list index of the reference picture, a reference picture index of the reference picture, and a quantization parameter (QP) of the reference picture.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of International Patent Application No. PCT/RU2020/050002 filed on Jan. 13, 2020, which claims priority to U.S. Provisional Patent Application No. 62/791,792 filed on Jan. 12, 2019. The disclosures of the aforementioned applications are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

Embodiments of the present application generally relate to the field of motion compensation by inter prediction.

BACKGROUND

Video coding (i.e., video encoding and decoding) is used in a wide range of digital video applications, for example broadcast digital television (TV), video transmission over Internet and mobile networks, real-time conversational applications such as video chat, video conferencing, DIGITAL VERSATILE DISC (DVD) and BLU-RAY DISCS, video content acquisition and editing systems, and camcorders of security applications.

The amount of video data needed to depict even a relatively short video can be substantial, which may result in difficulties when the data is to be streamed or otherwise communicated across a communications network with limited bandwidth capacity. Thus, video data is generally compressed before being communicated across modern day telecommunications networks. The size of a video could also be an issue when the video is stored on a storage device because memory resources may be limited. Video compression devices often use software and/or hardware at the source to code the video data prior to transmission or storage, thereby decreasing the quantity of data needed to represent digital video images. The compressed data is then received at the destination by a video decompression device that decodes the video data. With limited network resources and ever increasing demands of higher video quality, improved compression and decompression techniques that improve compression ratio with little to no sacrifice in picture quality are desirable.

SUMMARY OF THE DISCLOSURE

One embodiment of the present disclosure is a method of determining a distance table of a merge with motion vector difference (MMVD) mode, wherein the method comprises determining a reference picture from at least one reference picture list of a current processing unit based on at least one parameter of the reference picture, and obtaining the distance table for the current processing unit based on the reference picture, wherein the at least one parameter of the reference picture is selected from a group consisting of a picture order count (POC) number of the reference picture, a number of MMVD blocks of the reference picture, a reference picture list index of the reference picture, a reference picture index of the reference picture, and a quantization parameter (QP) of the reference picture.

The method may further comprise obtaining at least one candidate reference picture with a POC number closest to a POC number of the current processing unit, wherein the reference picture is determined from the at least one candidate reference picture. The POC number closest to the POC number of the current processing unit has the smallest absolute difference to the POC number of the current processing unit. In each reference picture list of the current processing unit, there may be up to two candidate reference pictures with POC numbers closest to the POC number of the current processing unit.

The method may further comprise obtaining at least one candidate reference picture with a smallest absolute QP difference to the current processing unit, wherein the reference picture is determined from the at least one candidate reference picture. The at least one candidate reference picture with the smallest absolute QP difference to the current processing unit may, in particular, be determined from among the at least one candidate reference picture with the POC number closest to the POC number of the current processing unit.

The method may further comprise obtaining at least one candidate reference picture with a smallest QP, wherein the reference picture is determined from the at least one candidate reference picture. The at least one candidate reference picture with the smallest QP may, in particular, be determined from among the at least one candidate reference picture with the smallest absolute QP difference to the current processing unit and/or from among the at least one candidate reference picture with the POC number closest to the POC number of the current processing unit.

The method may further comprise obtaining at least one candidate reference picture with a largest number of MMVD blocks, wherein the reference picture is determined from the at least one candidate reference picture. The at least one candidate reference picture with the largest number of MMVD blocks may, in particular, be determined from among the at least one candidate reference picture with the smallest QP and/or from among the at least one candidate reference picture with the smallest absolute QP difference to the current processing unit and/or from among the at least one candidate reference picture with the POC number closest to the POC number of the current processing unit.

The method may further comprise obtaining at least one candidate reference picture with a lowest reference picture list index, wherein the reference picture is determined from the at least one candidate reference picture. The at least one candidate reference picture with the lowest reference picture list index may, in particular, be determined from among the at least one candidate reference picture with the smallest QP and/or the at least one candidate reference picture with the largest number of MMVD blocks.

The method may further comprise obtaining at least one candidate reference picture with a lowest reference picture index, wherein the reference picture is determined from the at least one candidate reference picture. The at least one candidate reference picture with the lowest reference picture index may, in particular, be determined from among the at least one candidate reference picture with the lowest reference picture list index.

The reference picture may satisfy one of the following conditions:

condition 1: having a POC number closest to a POC number of the current processing unit among the reference pictures of the at least one reference picture list;

condition 2: having a smallest absolute QP difference to the current processing unit among the reference pictures of the at least one reference picture list;

condition 3: having a same reference picture list index as a motion vector predictor (MVP) of a current block in the current processing unit;

condition 4: having a same reference picture index as an MVP of the current block in the current processing unit;

condition 5: having a largest number of MMVD blocks among the reference pictures that satisfy at least one of condition 1, condition 2, condition 3, and condition 4;

condition 6: having a smallest QP among the reference pictures that satisfy at least one of condition 1, condition 2, condition 3, condition 4, and condition 5;

condition 7: having a lowest reference picture list index among the reference pictures that satisfy at least one of condition 1, condition 2, condition 3, condition 4, condition 5, and condition 6;

condition 8: having a lowest reference picture index among the reference pictures that satisfy at least one of condition 1, condition 2, condition 3, condition 4, condition 5, condition 6, and condition 7.

Another embodiment of the present disclosure is a method of determining a distance table of a MMVD mode, wherein the method comprises determining a previous coded picture of a current processing unit, wherein the previous coded picture and the current processing unit are in a same temporal layer, obtaining a usage statistics of a distance table of the previous coded picture, and determining a distance table for the current processing unit based on the usage statistics. A set of distance tables may be stored for each temporal layer. The distance table for the current processing unit may be added to the set of distance tables for the temporal layer of the current processing unit and the set of distance tables for the temporal layer above.

In the embodiments above, obtaining the distance table for the current processing unit based on the reference picture may comprise obtaining a default distance table for the current processing unit in the event that the reference picture is an intra frame.

Alternatively, obtaining the distance table for the current processing unit based on the reference picture may comprise retrieving a distance table for the reference picture as the distance table for the current processing unit.

In the embodiments above, the current processing unit may be a picture or a tile or a slice.

In the embodiments above, the number of MMVD blocks is a quantity of blocks coded by the MMVD mode.

Alternatively, the number of MMVD blocks is a quantity of square blocks coded by the MMVD mode.

In the embodiments above, the distance table may represent a relationship between an absolute value of a motion vector difference and a distance index, wherein information of the distance index is carried by a bitstream.

Another embodiment of the present disclosure is an encoder comprising processing circuitry for carrying out the method according to any one of the above embodiments.

Another embodiment of the present disclosure is a decoder comprising processing circuitry for carrying out the method according to any one of the above embodiments.

Another embodiment of the present disclosure is a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any one of the above embodiments.

Another embodiment of the present disclosure is a decoder comprising one or more processors, and a non-transitory computer-readable storage medium coupled to the one or more processors and storing instructions for execution by the one or more processors, wherein the instructions, when executed by the one or more processors, configure the decoder to carry out the method according to any one of the above embodiments.

Another embodiment of the present disclosure is an encoder comprising one or more processors, and a non-transitory computer-readable storage medium coupled to the one or more processors and storing instructions for execution by the one or more processors, wherein the instructions, when executed by the one or more processors, configure the encoder to carry out the method according to any one of the above embodiments.

The present disclosure further provides the aspect of a method of determining at least one distance table for motion compensation by inter prediction, wherein the method comprises determining at least one reference picture with a closest POC number to a current picture, based on a POC number of the current picture and POC numbers of pictures in at least one reference list of the current picture, and obtaining at least one distance table for the current picture based on the at least one reference picture with the closest POC number to the current picture.

When a quantity of the at least one reference picture with the closest POC number is greater than 1, obtaining at least one distance table for the current picture based on the at least one reference picture with the closest POC number to the current picture may comprise selecting at least one candidate reference picture from the at least one reference picture with the closest POC number based on a number of blocks with MMVD coding in each of the at least one reference picture with the closest POC number, and obtaining the at least one distance table for the current picture based on the at least one candidate reference picture. The at least one candidate reference picture may be selected according to the number of blocks with MMVD coding in the at least one candidate reference picture being largest as compared to the number of blocks with MMVD coding in each of the at least one reference picture with the closest POC number.

Alternatively, when a quantity of the at least one reference picture with the closest POC number is greater than 1, obtaining at least one distance table for the current picture based on the at least one reference picture with the closest POC number to the current picture may comprise selecting at least one candidate reference picture from the at least one reference picture with the closest POC number, based on a number of blocks with MMVD coding in each of the at least one reference picture with the closest POC number and the at least one reference list of the current picture, and obtaining the at least one distance table for the current picture based on the at least one candidate reference picture. The at least one candidate reference picture may be selected according to the number of blocks with MMVD coding in the at least one candidate reference picture being largest as compared to the number of blocks with MMVD coding in each of the at least one reference picture with the closest POC number and further selecting the at least one candidate reference picture in a reference list having a lowest list number.

Alternatively, when a quantity of the at least one reference picture with the closest POC number is greater than 1, obtaining at least one distance table for the current picture based on the at least one reference picture with the closest POC number to the current picture may comprise selecting a final reference picture from the at least one reference picture with the closest POC number, based on a number of blocks with MMVD coding in each of the at least one reference picture with the closest POC number, the at least one reference list of the current picture and a reference index of the at least one reference picture with the closest POC number, and obtaining the at least one distance table for the current picture based on the final reference picture. The final reference picture may be selected according to the number of blocks with MMVD coding in the final reference picture being largest as compared to the number of blocks with MMVD coding in each of the at least one reference picture with the closest POC number and further selecting the final reference picture having a lower reference index in a reference list having a lowest list number.

In the method according to any of the above aspects, when a prediction mode of the at least one reference picture with the closest POC number to the current picture is intra prediction, the at least one distance table for the current picture may be at least one default distance table.

In the method according to the first aspect, when a quantity of the at least one reference picture with the closest POC number is greater than 1, obtaining at least one distance table for the current picture based on the at least one reference picture with the closest POC number to the current picture may comprise selecting at least one candidate reference picture from the at least one reference picture with the closest POC number based on a number of square blocks with MMVD coding in each of the at least one reference picture with the closest POC number, and obtaining the at least one distance table for the current picture based on the at least one candidate reference picture. The at least one candidate reference picture may be selected according to the number of square blocks with MMVD coding in the at least one candidate reference picture being largest as compared to the number of square blocks with MMVD coding in each of the at least one reference picture with the closest POC number.

In the method according to the first aspect, when a quantity of the at least one reference picture with the closest POC number is greater than 1, obtaining at least one distance table for the current picture based on the at least one reference picture with the closest POC number to the current picture may comprise selecting at least one candidate reference picture from the at least one reference picture with the closest POC number, based on a number of square blocks with MMVD coding in each of the at least one reference picture with the closest POC number and the at least one reference list of the current picture, and obtaining the at least one distance table for the current picture based on the at least one candidate reference picture. The at least one candidate reference picture may be selected according to the number of square blocks with MMVD coding in the at least one candidate reference picture being largest as compared to the number of square blocks with MMVD coding in each of the at least one reference picture with the closest POC number and further selecting the at least one candidate reference picture in a reference list having a lowest list number.

In the method according to the first aspect, when a quantity of the at least one reference picture with the closest POC number is greater than 1, obtaining at least one distance table for the current picture based on the at least one reference picture with the closest POC number to the current picture may comprise selecting a final reference picture from the at least one reference picture with the closest POC number, based on a number of square blocks with MMVD coding in each of the at least one reference picture with the closest POC number, the at least one reference list of the current picture and a reference index of the at least one reference picture with the closest POC number, and obtaining the at least one distance table for the current picture based on the final reference picture. The final reference picture may be selected according to the number of square blocks with MMVD coding in the final reference picture being largest as compared to the number of blocks with MMVD coding in each of the at least one reference picture with the closest POC number and further selecting the final reference picture having a lower reference index in a reference list having a lowest list number.

In the method according to the first aspect, when a quantity of the at least one reference picture with the closest POC number is greater than 1, obtaining at least one distance table for the current picture based on the at least one reference picture with the closest POC number to the current picture may comprise selecting at least one candidate reference picture from the at least one reference picture with the closest POC number based on a QP in each of the at least one reference picture with the closest POC number, and obtaining the at least one distance table for the current picture based on the at least one candidate reference picture. The at least one candidate reference picture may be selected according to the QP in the at least one candidate reference picture being smallest as compared to the QP in each of the at least one reference picture with the closest POC number.

In the method according to the first aspect, when a quantity of the at least one reference picture with the closest POC number is greater than 1, obtaining at least one distance table for the current picture based on the at least one reference picture with the closest POC number to the current picture may comprise selecting at least one candidate reference picture from the at least one reference picture with the closest POC number, based on a QP in each of the at least one reference picture with the closest POC number and the at least one reference list of the current picture, and obtaining the at least one distance table for the current picture based on the at least one candidate reference picture. The at least one candidate reference picture may be selected according to the QP in the at least one candidate reference picture being smallest as compared to the QP in each of the at least one reference picture with the closest POC number and further selecting the at least one candidate reference picture in a reference list having a lowest list number.

In the method according to the first aspect, when a quantity of the at least one reference picture with the closest POC number is greater than 1, obtaining at least one distance table for the current picture based on the at least one reference picture with the closest POC number to the current picture may comprise selecting a final reference picture from the at least one reference picture with the closest POC number, based on a QP in each of the at least one reference picture with the closest POC number, the at least one reference list of the current picture and a reference index of the at least one reference picture with the closest POC number, and obtaining the at least one distance table for the current picture based on the final reference picture. The final reference picture may be selected according to the QP in the final reference picture being smallest as compared to the QP in each of the at least one reference picture with the closest POC number and further selecting the final reference picture having a lower reference index in a reference list having a lowest list number.

Another aspect of the present disclosure is a method of determining at least one distance table for motion compensation by inter prediction, wherein the method comprises determining at least one reference picture with a closest QP to a current picture, based on a QP of the current picture and QPs of pictures in at least one reference list of the current picture, and obtaining at least one distance table for the current picture based on the at least one reference picture with the closest QP to the current picture.

When a quantity of the at least one reference picture with the closest QP is greater than 1, obtaining at least one distance table for the current picture based on the at least one reference picture with the closest QP to the current picture may comprises selecting at least one candidate reference picture from the at least one reference picture with the closest QP based on the QP in each of the at least one reference picture with the closest QP, and obtaining the at least one distance table for the current picture based on the at least one candidate reference picture. The at least one candidate reference picture may be selected according to the QP in the at least one candidate reference picture being smallest as compared to the QP in each of the at least one reference picture with the closest QP.

Alternatively, when a quantity of the at least one reference picture with the closest QP is greater than 1, obtaining at least one distance table for the current picture based on the at least one reference picture with the closest QP to the current picture may comprise selecting at least one candidate reference picture from the at least one reference picture with the closest QP based on the QP in each of the at least one reference picture with the closest QP and the at least one reference list of the current picture, and obtaining the at least one distance table for the current picture based on the at least one candidate reference picture. The at least one candidate reference picture may be selected according to the QP in the at least one candidate reference picture being smallest as compared to the QP in each of the at least one reference picture with the closest QP and further selecting the at least one candidate reference picture in a reference list having a lowest list number.

Alternatively, when a quantity of the at least one reference picture with the closest QP is greater than 1, obtaining at least one distance table for the current picture based on the at least one reference picture with the closest QP to the current picture may comprise selecting a final reference picture from the at least one reference picture with the closest QP based on the QP in each of the at least one reference picture with the closest QP, the at least one reference list of the current picture and a reference index of the at least one reference picture with the closest QP, and obtaining the at least one distance table for the current picture based on the final reference picture. The final reference picture may be selected according to the QP in the final reference picture being smallest as compared to the QP in each of the at least one reference picture with the closest QP and further selecting the final reference picture having a lower reference index in a reference list having a lowest list number.

In the method according to the previous aspect, when a prediction mode of the at least one reference picture with the closest QP to a current picture is intra prediction, the at least one distance table for the current picture may be at least one default distance table.

Another aspect of the present disclosure is a method of determining at least one distance table for motion compensation by inter prediction, wherein the method comprises determining at least one reference picture referred to by a reference index of at least one selected MVP candidate of a current block of a current picture, and retrieving the at least one distance table from the at least one reference picture.

Another aspect of the present disclosure is a method of determining at least one distance table for motion compensation by inter prediction, wherein the method comprises using at least one distance table from a previous picture in a same temporal layer in decoding order for a current picture, and determining a new distance table for the current picture based on statistics of using entries from the at least one distance table during processing of the current picture.

Another aspect of the present disclosure is a method of determining at least one distance table for motion compensation by inter prediction, wherein the method comprises determining at least one initial distance table according to the method of any one of the preceding aspects for a tile of a current picture, and modifying the at least one initial distance table during processing of the tile.

Another aspect of the present disclosure is a method of constructing motion information for motion compensation by inter prediction, wherein the method comprises constructing a set of motion information candidates based on a set of potential candidates, wherein the set of motion information candidates and the set of potential candidates each comprise one or more motion vectors, wherein constructing the set of motion information candidates comprises computing each motion vector included in the set of motion information candidates as a vector sum of a motion vector included in the set of potential candidates and a motion vector difference, wherein the set of motion information candidates is a MMVD, MVP, candidate list, wherein the motion vector difference comprises a distance between a position pointed to by a candidate from the set of potential candidates and a target point and a direction from the position to the target point, and wherein the motion vector difference is encoded based on a distance table determined according to the method of any one of the preceding aspects.

The present disclosure further provides an encoder comprising processing circuitry for carrying out the method according to any one of the preceding aspects.

The present disclosure further provides a decoder comprising processing circuitry for carrying out the method according to any one of the preceding aspects.

The present disclosure further provides a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any one of the preceding aspects.

The present disclosure further provides a decoder, comprising one or more processors, and a non-transitory computer-readable storage medium coupled to the one or more processors and storing instructions for execution by the one or more processors, wherein the instructions, when executed by the one or more processors, configure the decoder to carry out the method according to any one of the preceding aspects.

The present disclosure further provides an encoder, comprising one or more processors, and a non-transitory computer-readable storage medium coupled to the one or more processors and storing instructions for execution by the one or more processors, wherein the instructions, when executed by the one or more processors, configure the encoder to carry out the method according to any one of the preceding aspects.

Using reference pictures with the closest POC number may exploit the temporal correlation between the current picture and the reference picture. A large number of square blocks with MMVD coding may improve the significance of the statistics for re-ordering the distance table. A lower reference picture list index may prefer a forward prediction of the prediction block. A lower reference picture index may reduce the signaling amount. A smaller QP may reduce the losses during quantization due to a smaller quantization step size.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, embodiments of the disclosure are described in more detail with reference to the attached figures and drawings.

FIG. 1A is a block diagram showing an example of a video coding system configured to implement embodiments of the disclosure.

FIG. 1B is a block diagram showing another example of a video coding system configured to implement embodiments of the disclosure.

FIG. 2 is a block diagram showing an example of a video encoder configured to implement embodiments of the disclosure.

FIG. 3 is a block diagram showing an example structure of a video decoder configured to implement embodiments of the disclosure.

FIG. 4 is a block diagram illustrating an example of an encoding apparatus or a decoding apparatus.

FIG. 5 is a block diagram illustrating another example of an encoding apparatus or a decoding apparatus.

FIG. 6 is a flow chart illustrating an example of a method of determining a distance table.

FIG. 7 is a flow chart illustrating another example of a method of determining a distance table.

In the following, identical reference signs refer to identical or at least functionally equivalent features if not explicitly specified otherwise.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the disclosure, or specific aspects in which embodiments of the present disclosure, may be used. It is understood that embodiments of the disclosure, may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure, is defined by the appended claims.

For instance, it is understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically noted otherwise.

Video coding typically refers to the processing of a sequence of pictures, which form the video or video sequence. Instead of the term “picture”, the term “frame” or “image” may be used as synonyms in the field of video coding. Video coding (or coding in general) comprises two parts: video encoding and video decoding. Video encoding is performed at the source side, typically comprising processing (e.g. by compression) the original video pictures to reduce the amount of data required for representing the video pictures (for more efficient storage and/or transmission). Video decoding is performed at the destination side and typically comprises the inverse processing compared to the encoder to reconstruct the video pictures. Embodiments referring to “coding” of video pictures (or pictures in general) shall be understood to relate to “encoding” or “decoding” of video pictures or respective video sequences. The combination of the encoding part and the decoding part is also referred to as CODEC.

In case of lossless video coding, the original video pictures can be reconstructed, i.e. the reconstructed video pictures have the same quality as the original video pictures (assuming no transmission loss or other data loss occurs during storage or transmission). In case of lossy video coding, further compression, e.g. by quantization, is performed, to reduce the amount of data representing the video pictures, which cannot be completely reconstructed at the decoder, i.e. the quality of the reconstructed video pictures is lower or worse compared to the quality of the original video pictures.

Several video coding standards belong to the group of “lossy hybrid video codecs” (i.e. combine spatial and temporal prediction in the sample domain and two-dimensional (2D) transform coding for applying quantization in the transform domain). Each picture of a video sequence is typically partitioned into a set of non-overlapping blocks and the coding is typically performed on a block level. In other words, at the encoder the video is typically processed, i.e. encoded, on a block (video block) level, e.g. by using spatial (intra picture) prediction and/or temporal (inter picture) prediction to generate a prediction block, subtracting the prediction block from the current block (block currently processed/to be processed) to obtain a residual block, transforming the residual block and quantizing the residual block in the transform domain to reduce the amount of data to be transmitted (compression), whereas at the decoder the inverse processing compared to the encoder is applied to the encoded or compressed block to reconstruct the current block for representation. Furthermore, the encoder duplicates the decoder processing loop such that both will generate identical predictions (e.g. intra- and inter predictions) and/or reconstructions for processing, i.e. coding, the subsequent blocks.

In the following embodiments of a video coding system 10, a video encoder 20 and a video decoder 30 are described based on FIGS. 1 to 3

FIG. 1A is a schematic block diagram illustrating an example coding system 10, e.g. a video coding system 10 (or coding system 10) that may utilize techniques of this present application. Video encoder 20 (or encoder 20) and video decoder 30 (or decoder 30) of video coding system 10 represent examples of devices that may be configured to perform techniques in accordance with various examples described in the present application.

As shown in FIG. 1A, the coding system 10 comprises a source device 12 configured to provide encoded picture data 21 e.g. to a destination device 14 for decoding the encoded picture data 13.

The source device 12 comprises an encoder 20, and may additionally, i.e. optionally, comprise a picture source 16, a pre-processor (or pre-processing unit) 18, e.g. a picture pre-processor 18, and a communication interface or communication unit 22.

The picture source 16 may comprise or be any kind of picture capturing device, for example a camera for capturing a real-world picture, and/or any kind of a picture generating device, for example a computer-graphics processor for generating a computer animated picture, or any kind of other device for obtaining and/or providing a real-world picture, a computer generated picture (e.g. a screen content, a virtual reality (VR) picture) and/or any combination thereof (e.g. an augmented reality (AR) picture). The picture source may be any kind of memory or storage storing any of the aforementioned pictures.

In distinction to the pre-processor 18 and the processing performed by the pre-processing unit 18, the picture or picture data 17 may also be referred to as raw picture or raw picture data 17.

Pre-processor 18 may be configured to receive the (raw) picture data 17 and to perform pre-processing on the picture data 17 to obtain a pre-processed picture 19 or pre-processed picture data 19. Pre-processing performed by the pre-processor 18 may, e.g., comprise trimming, color format conversion (e.g. from red, green, and blue (RGB) to luma, blue-difference chroma, and red-difference chroma (YCbCr)), color correction, or de-noising. It can be understood that the pre-processing unit 18 may be an optional component.

The video encoder 20 may be configured to receive the pre-processed picture data 19 and provide encoded picture data 21 (further details will be described below, e.g., based on FIG. 2).

Communication interface 22 of the source device 12 may be configured to receive the encoded picture data 21 and to transmit the encoded picture data 21 (or any further processed version thereof) over communication channel 13 to another device, e.g. the destination device 14 or any other device, for storage or direct reconstruction.

The destination device 14 comprises a decoder 30 (e.g. a video decoder 30), and may additionally, i.e. optionally, comprise a communication interface or communication unit 28, a post-processor 32 (or post-processing unit 32) and a display device 34.

The communication interface 28 of the destination device 14 may be configured to receive the encoded picture data 21 (or any further processed version thereof), e.g. directly from the source device 12 or from any other source, e.g. a storage device, such as an encoded picture data storage device, and provide the encoded picture data 21 to the decoder 30.

The communication interface 22 and the communication interface 28 may be configured to transmit or receive the encoded picture data 21 or encoded data 13 via a direct communication link between the source device 12 and the destination device 14, e.g. a direct wired or wireless connection, or via any kind of network, e.g. a wired or wireless network or any combination thereof, or any kind of private and public network, or any kind of combination thereof.

The communication interface 22 may be configured to package the encoded picture data 21 into an appropriate format, e.g. packets, and/or process the encoded picture data using any kind of transmission encoding or processing for transmission over a communication link or communication network.

The communication interface 28, forming the counterpart of the communication interface 22, may be configured to receive the transmitted data and process the transmission data using any kind of corresponding transmission decoding or processing and/or de-packaging to obtain the encoded picture data 21.

Both, communication interface 22 and communication interface 28 may be configured as unidirectional communication interfaces as indicated by the arrow for the communication channel 13 in FIG. 1A pointing from the source device 12 to the destination device 14, or as bi-directional communication interfaces, and may be configured to send and receive messages, e.g. to set up a connection, to acknowledge and exchange any other information related to the communication link and/or data transmission, such as encoded picture data transmission.

The decoder 30 may be configured to receive the encoded picture data 21 and provide decoded picture data 31 or a decoded picture 31 (further details will be described below, e.g., based on FIG. 3 or FIG. 5). The post-processor 32 of destination device 14 may be configured to post-process the decoded picture data 31 (also called reconstructed picture data), e.g. the decoded picture 31, to obtain post-processed picture data 33, such as a post-processed picture 33. The post-processing performed by the post-processing unit 32 may comprise any one or more of color format conversion (e.g. from YCbCr to RGB), color correction, trimming, or re-sampling, or any other processing, e.g. for preparing the decoded picture data 31 for display, e.g. by display device 34.

The display device 34 of the destination device 14 may be configured to receive the post-processed picture data 33 for displaying the picture, e.g. to a user or viewer. The display device 34 may be or comprise any kind of display for representing the reconstructed picture, such as an integrated or external display or monitor. The display may be a liquid-crystal displays (LCDs), an organic light-emitting diodes (LEDs) (OLEDs) display, a plasma display, a projector, a micro LED display, a liquid crystal on silicon (LCoS), a digital light processor (DLP) or any kind of other display.

Although FIG. 1A depicts the source device 12 and the destination device 14 as separate devices, embodiments of devices may also comprise both devices or both functionalities, i.e. the source device 12 or corresponding functionality and the destination device 14 or corresponding functionality. In such embodiments the source device 12 or corresponding functionality and the destination device 14 or corresponding functionality may be implemented using the same hardware and/or software or by separate hardware and/or software or any combination thereof.

As will be apparent for the skilled person based on the description, the existence and (exact) split of functionalities of the different units or functionalities within the source device 12 and/or destination device 14 as shown in FIG. 1A may vary depending on the actual device and application.

The encoder 20 (e.g. a video encoder 20) or the decoder 30 (e.g. a video decoder 30) or both, encoder 20 and decoder 30 may be implemented via processing circuitry as shown in FIG. 1B, such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), discrete logic, hardware, video coding dedicated or any combinations thereof. The encoder 20 may be implemented via processing circuitry 46 to embody the various modules as discussed with respect to encoder 20 of FIG. 2 and/or any other encoder system or subsystem described herein. The decoder 30 may be implemented via processing circuitry 46 to embody the various modules as discussed with respect to decoder 30 of FIG. 3 and/or any other decoder system or subsystem described herein. The processing circuitry may be configured to perform the various operations as discussed later. As shown in FIG. 5, if the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable storage medium and may execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Video encoder 20 and video decoder 30 may be integrated as part of a combined encoder/decoder (CODEC) in a single device, for example, as shown in FIG. 1B.

The video coding system 40 shown in FIG. 1B comprises a processing circuitry implementing both a video encoder 20 and a video decoder 30. In addition, one or more imaging devices 41, such as a camera for capturing real-world pictures, an antenna 42, one or more memory stores 44, one or more processors 43 and/or a display device 45, such the display device 34 described above, may be provided as part of the video coding system 40.

Source device 12 and destination device 14 may comprise any of a wide range of devices, including any kind of handheld or stationary devices, e.g. notebook or laptop computers, mobile phones, smart phones, tablets or tablet computers, cameras, desktop computers, set-top boxes, televisions, display devices, digital media players, video gaming consoles, video streaming devices (such as content services servers or content delivery servers), broadcast receiver devices, broadcast transmitter devices, or the like and may use no or any kind of operating system. In some cases, the source device 12 and the destination device 14 may be equipped for wireless communication. Thus, the source device 12 and the destination device 14 may be wireless communication devices.

In some cases, video coding system 10 illustrated in FIG. 1A is merely an example and the techniques of the present application may apply to video coding systems (e.g., video encoding or video decoding) that do not necessarily include any data communication between the encoding and decoding devices. In other examples, data is retrieved from a local memory, streamed over a network, or the like. A video encoding device may encode and store data in memory, and/or a video decoding device may retrieve and decode data from memory. In some examples, the encoding and decoding is performed by devices that do not communicate with one another, but simply encode data to memory and/or retrieve and decode data from memory.

For convenience of description, embodiments of the disclosure, are described herein, for example, by reference to High Efficiency Video Coding (HEVC) or to the reference software of Versatile Video coding (VVC), the next generation video coding standard developed by the Joint Collaboration Team on Video Coding (JCT-VC) of International Telecommunication Union (ITU) Telecommunication Standardization Sector (ITU-T) Video Coding Experts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG). One of ordinary skill in the art will understand that embodiments of the disclosure, are not limited to HEVC or VVC.

Encoder and Encoding Method:

FIG. 2 shows a schematic block diagram of an example video encoder 20 that is configured to implement the techniques of the present application. In the example of FIG. 2, the video encoder 20 comprises an input 201 (or input interface 201), a residual calculation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, and an inverse transform processing unit 212, a reconstruction unit 214, a loop filter unit 220, a decoded picture buffer (DPB) 230, a mode selection unit 260, an entropy encoding unit 270 and an output 272 (or output interface 272). The mode selection unit 260 may include an inter prediction unit 244, an intra prediction unit 254 and a partitioning unit 262. The inter prediction unit 244 may include a motion estimation unit and a motion compensation unit (not shown). A video encoder 20 as shown in FIG. 2 may also be referred to as a hybrid video encoder or a video encoder according to a hybrid video codec.

The residual calculation unit 204, the transform processing unit 206, the quantization unit 208, and the mode selection unit 260 may be referred to as forming a forward signal path of the encoder 20, whereas the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the loop filter 220, the DPB 230, the inter prediction unit 244 and the intra-prediction unit 254 may be referred to as forming a backward signal path of the video encoder 20, wherein the backward signal path of the video encoder 20 corresponds to the signal path of the decoder (see video decoder 30 in FIG. 3). The inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the loop filter 220, the DPB 230, the inter prediction unit 244 and the intra-prediction unit 254 are also referred to forming the “built-in decoder” of video encoder 20.

Pictures & Picture Partitioning (Pictures & Blocks):

The encoder 20 may be configured to receive, e.g. via input 201, a picture 17 (or picture data 17), e.g. a picture of a sequence of pictures forming a video or video sequence. The received picture or picture data may also be a pre-processed picture 19 (or pre-processed picture data 19). For the sake of simplicity, the following description refers to the picture 17. The picture 17 may also be referred to as a current picture or a picture to be coded (in particular, in video coding to distinguish the current picture from other pictures, e.g. previously encoded and/or decoded pictures of the same video sequence, i.e. the video sequence which also comprises the current picture).

A (digital) picture is or can be regarded as a two-dimensional array or matrix of samples with intensity values. A sample in the array may also be referred to as pixel (short form of picture element) or a pel. The number of samples in the horizontal and vertical direction (or axis) of the array or picture defines the size and/or resolution of the picture. For representation of color, typically three color components are employed, i.e. the picture may be represented as or include three sample arrays. In RBG format or color space, a picture comprises a corresponding red, green and blue sample array. However, in video coding each pixel is typically represented in a luminance and chrominance format or color space, e.g. YCbCr, which comprises a luminance component indicated by Y (sometimes also L is used instead) and two chrominance components indicated by Cb and Cr. The luminance (or luma) component Y represents the brightness or grey level intensity (e.g. like in a grey-scale picture), while the two chrominance (or chroma) components Cb and Cr represent the chromaticity or color information components. Accordingly, a picture in YCbCr format comprises a luminance sample array of luminance sample values (Y), and two chrominance sample arrays of chrominance values (Cb and Cr). Pictures in RGB format may be converted or transformed into YCbCr format and vice versa. The process is also known as color transformation or conversion. If a picture is monochrome, the picture may comprise only a luminance sample array. Accordingly, a picture may be, for example, an array of luma samples in monochrome format or an array of luma samples and two corresponding arrays of chroma samples in 4:2:0, 4:2:2, and 4:4:4 color format.

Embodiments of the video encoder 20 may comprise a picture partitioning unit (not depicted in FIG. 2) configured to partition the picture 17 into a plurality of (typically non-overlapping) picture blocks 203. These blocks may also be referred to as root blocks, macro blocks (H.264/Advanced Video Coding (AVC)) or coding tree blocks (CTBs) or coding tree units (CTUs) (according to H.265/HEVC and VVC). The picture partitioning unit may be configured to use the same block size for all pictures of a video sequence and the corresponding grid defining the block size, or to change the block size between pictures or subsets or groups of pictures, and partition each picture into the corresponding blocks.

In further embodiments, the video encoder may be configured to receive directly a block 203 of the picture 17, e.g. one, several or all blocks forming the picture 17. The picture block 203 may also be referred to as current picture block or picture block to be coded.

Like the picture 17, the picture block 203 is or can be regarded as a two-dimensional array or matrix of samples with intensity values (sample values), although of smaller dimension than the picture 17. In other words, the block 203 may comprise, e.g., one sample array (e.g. a luma array in case of a monochrome picture 17, or a luma or chroma array in case of a color picture) or three sample arrays (e.g. a luma and two chroma arrays in case of a color picture 17) or any other number and/or kind of arrays depending on the color format applied. The number of samples in the horizontal and vertical direction (or axis) of the block 203 defines the size of the block 203. Accordingly, a block may, for example, comprise an M×N (M-column by N-row) array of samples, or an M×N array of transform coefficients.

Embodiments of the video encoder 20 as shown in FIG. 2 may be configured to encode the picture 17 block by block, e.g. the encoding and prediction is performed per block 203.

Embodiments of the video encoder 20 as shown in FIG. 2 may be further configured to partition and/or encode the picture by using slices (or as video slices), wherein a picture may be partitioned into or encoded using one or more slices (typically non-overlapping), and each slice may comprise one or more blocks (e.g. CTUs).

Embodiments of the video encoder 20 as shown in FIG. 2 may be further configured to partition and/or encode the picture by using tile groups (or video tile groups) and/or tiles (or as video tiles), wherein a picture may be partitioned into or encoded using one or more tile groups (typically non-overlapping), and each tile group may comprise one or more blocks (e.g. CTUs) or one or more tiles, wherein each tile may be of rectangular shape and may comprise one or more blocks (e.g. CTUs), e.g. complete or fractional blocks.

Residual Calculation:

The residual calculation unit 204 may be configured to calculate a residual block 205 (or as residual 205) based on the picture block 203 and a prediction block 265 (further details about the prediction block 265 are provided later), e.g. by subtracting sample values of the prediction block 265 from sample values of the picture block 203, sample by sample (pixel by pixel) to obtain the residual block 205 in the sample domain.

Transform:

The transform processing unit 206 may be configured to apply a transform, such as a discrete cosine transform (DCT) or discrete sine transform (DST), on the sample values of the residual block 205 to obtain transform coefficients 207 in a transform domain. The transform coefficients 207 may also be referred to as transform residual coefficients and represent the residual block 205 in the transform domain.

The transform processing unit 206 may be configured to apply integer approximations of DCT/DST, such as the transforms specified for H.265/HEVC. Compared to an orthogonal DCT transform, such integer approximations are typically scaled by a certain factor. In order to preserve the norm of the residual block which is processed by forward and inverse transforms, additional scaling factors are applied as part of the transform process. The scaling factors are typically chosen based on certain constraints like scaling factors being a power of two for shift operations, bit depth of the transform coefficients, tradeoff between accuracy and implementation costs, etc. Specific scaling factors are, for example, specified for the inverse transform, e.g. by inverse transform processing unit 212 (and the corresponding inverse transform, e.g. by inverse transform processing unit 312 at video decoder 30) and corresponding scaling factors for the forward transform, e.g. by transform processing unit 206, at an encoder 20 may be specified accordingly.

Embodiments of the video encoder 20 (respectively, the transform processing unit 206) may be configured to output transform parameters, e.g. a type of transform or transforms, e.g. directly or encoded or compressed via the entropy encoding unit 270, so that, e.g., the video decoder 30 may receive and use the transform parameters for decoding.

Quantization:

The quantization unit 208 may be configured to quantize the transform coefficients 207 to obtain quantized coefficients 209, e.g. by applying scalar quantization or vector quantization. The quantized coefficients 209 may also be referred to as quantized transform coefficients 209 or quantized residual coefficients 209.

The quantization process may reduce the bit depth associated with some or all of the transform coefficients 207. For example, an n-bit transform coefficient may be rounded down to an m-bit transform coefficient during quantization, where n is greater than m. The degree of quantization may be modified by adjusting a QP. For example, for scalar quantization, different scalings may be applied to achieve finer or coarser quantization. Smaller quantization step sizes correspond to finer quantization, whereas larger quantization step sizes correspond to coarser quantization. The applicable quantization step size may be indicated by a QP. The QP may, for example, be an index of a predefined set of applicable quantization step sizes. For example, small QPs may correspond to fine quantization (small quantization step sizes) and large QPs may correspond to coarse quantization (large quantization step sizes) or vice versa. The quantization may include division by a quantization step size and a corresponding and/or the inverse dequantization, e.g. by inverse quantization unit 210, may include multiplication by the quantization step size. Embodiments according to some standards, e.g. HEVC, may be configured to use a QP to determine the quantization step size. Generally, the quantization step size may be calculated based on a QP using a fixed point approximation of an equation including division. Additional scaling factors may be introduced for quantization and dequantization to restore the norm of the residual block, which might get modified because of the scaling used in the fixed point approximation of the equation for quantization step size and QP. In one embodiment, the scaling of the inverse transform and dequantization might be combined. Alternatively, customized quantization tables may be used and signaled from an encoder to a decoder, e.g. in a bitstream. The quantization is a lossy operation, wherein the loss increases with increasing quantization step sizes.

Embodiments of the video encoder 20 (respectively, the quantization unit 208) may be configured to output QPs, e.g. directly or encoded via the entropy encoding unit 270, so that, e.g., the video decoder 30 may receive and apply the QPs for decoding.

Inverse Quantization:

The inverse quantization unit 210 is configured to apply the inverse quantization of the quantization unit 208 on the quantized coefficients to obtain dequantized coefficients 211, e.g. by applying the inverse of the quantization scheme applied by the quantization unit 208 based on or using the same quantization step size as the quantization unit 208. The dequantized coefficients 211 may also be referred to as dequantized residual coefficients 211 and correspond—although typically not identical to the transform coefficients due to the loss by quantization—to the transform coefficients 207.

Inverse Transform:

The inverse transform processing unit 212 is configured to apply the inverse transform of the transform applied by the transform processing unit 206, e.g. an inverse DCT or inverse DST or other inverse transforms, to obtain a reconstructed residual block 213 (or corresponding dequantized coefficients 213) in the sample domain. The reconstructed residual block 213 may also be referred to as a transform block 213.

Reconstruction:

The reconstruction unit 214 (e.g. adder or summer 214) is configured to add the transform block 213 (i.e. reconstructed residual block 213) to the prediction block 265 to obtain a reconstructed block 215 in the sample domain, e.g. by adding—sample by sample—the sample values of the reconstructed residual block 213 and the sample values of the prediction block 265.

Filtering:

The loop filter unit 220 (or loop filter 220), is configured to filter the reconstructed block 215 to obtain a filtered block 221, or in general, to filter reconstructed samples to obtain filtered samples. The loop filter unit may be configured to smooth pixel transitions, or otherwise improve the video quality. The loop filter unit 220 may comprise one or more loop filters such as a de-blocking filter, a sample-adaptive offset (SAO) filter or one or more other filters, such as a bilateral filter, an adaptive loop filter (ALF), a sharpening, a smoothing filter or a collaborative filter, or any combination thereof. Although the loop filter unit 220 is shown in FIG. 2 as being an in-loop filter, in other configurations, the loop filter unit 220 may be implemented as a post loop filter. The filtered block 221 may also be referred to as a filtered reconstructed block 221.

Embodiments of the video encoder 20 (respectively, the loop filter unit 220) may be configured to output loop filter parameters (such as sample adaptive offset information), e.g. directly or encoded via the entropy encoding unit 270, so that, e.g., a decoder 30 may receive and apply the same loop filter parameters or respective loop filters for decoding.

DPB:

The DPB 230 may be a memory that stores reference pictures, or in general reference picture data, for encoding video data by video encoder 20. The DPB 230 may be formed by any of a variety of memory devices, such as dynamic random-access memory (RAM) (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAIVI), or other types of memory devices. The DPB 230 may be configured to store one or more filtered blocks 221. The DPB 230 may be further configured to store other previously filtered blocks, e.g. previously reconstructed and filtered blocks 221, of the same current picture or of different pictures, e.g. previously reconstructed pictures, and may provide complete previously reconstructed, i.e. decoded, pictures (and corresponding reference blocks and samples) and/or a partially reconstructed current picture (and corresponding reference blocks and samples), for example for inter prediction. The DPB 230 may also be configured to store one or more unfiltered reconstructed blocks 215, or in general unfiltered reconstructed samples, e.g. if the reconstructed block 215 is not filtered by loop filter unit 220, or any other further processed version of the reconstructed blocks or samples.

Mode Selection (Partitioning & Prediction):

The mode selection unit 260 comprises partitioning unit 262, inter-prediction unit 244 and intra-prediction unit 254, and is configured to receive or obtain original picture data, such as an original block 203 (current block 203 of the current picture 17), and reconstructed picture data, such as filtered and/or unfiltered reconstructed samples or blocks of the same (current) picture and/or from one or a plurality of previously decoded pictures, e.g. from DPB 230 or other buffers (e.g. line buffer, not shown). The reconstructed picture data is used as reference picture data for prediction, e.g. inter-prediction or intra-prediction, to obtain a prediction block 265 or predictor 265.

Mode selection unit 260 may be configured to determine or select a partitioning for a current block prediction mode (including no partitioning) and a prediction mode (e.g. an intra- or inter-prediction mode) and generate a corresponding prediction block 265, which is used for the calculation of the residual block 205 and for the reconstruction of the reconstructed block 215.

Embodiments of the mode selection unit 260 may be configured to select the partitioning and the prediction mode (e.g. from those supported by or available for mode selection unit 260), which provide the best match or in other words the minimum residual (minimum residual means better compression for transmission or storage), or a minimum signaling overhead (minimum signaling overhead means better compression for transmission or storage), or which considers or balances both. The mode selection unit 260 may be configured to determine the partitioning and prediction mode based on rate distortion optimization (RDO), i.e. select the prediction mode which provides a minimum rate distortion. Terms like “best”, “minimum”, “optimum” etc. in this context do not necessarily refer to an overall “best”, “minimum”, “optimum”, etc. but may also refer to the fulfillment of a termination or selection criterion like a value exceeding or falling below a threshold or other constraints leading potentially to a “sub-optimum selection” but reducing complexity and processing time.

In other words, the partitioning unit 262 may be configured to partition the block 203 into smaller block partitions or sub-blocks (which again form blocks), e.g. iteratively using quad-tree (QT)-partitioning, binary-tree (BT) partitioning, or triple-tree (TT)-partitioning or any combination thereof, and to perform the prediction for each of the block partitions or sub-blocks, wherein the mode selection comprises the selection of the tree-structure of the partitioned block 203 and the prediction modes are applied to each of the block partitions or sub-blocks.

In the following, the partitioning (e.g. by partitioning unit 262) and prediction processing (by inter-prediction unit 244 and intra-prediction unit 254) performed by an example video encoder 20 will be explained in more detail.

Partitioning:

The partitioning unit 262 may partition (or split) a current block 203 into smaller partitions, e.g. smaller blocks of square or rectangular size. These smaller blocks (which may also be referred to as sub-blocks) may be further partitioned into even smaller partitions. This is also referred to as tree-partitioning or hierarchical tree-partitioning, wherein a root block, e.g. at root tree-level 0 (hierarchy-level 0, depth 0), may be recursively partitioned, e.g. partitioned into two or more blocks of a next lower tree-level, e.g. nodes at tree-level 1 (hierarchy-level 1, depth 1), wherein these blocks may be again partitioned into two or more blocks of a next lower level, e.g. tree-level 2 (hierarchy-level 2, depth 2), etc. until the partitioning is terminated, e.g. because a termination criterion is fulfilled, e.g. a maximum tree depth or minimum block size is reached. Blocks which are not further partitioned are also referred to as leaf-blocks or leaf nodes of the tree. A tree using partitioning into two partitions is referred to as a BT, a tree using partitioning into three partitions is referred to as a TT, and a tree using partitioning into four partitions is referred to as a QT.

As mentioned before, the term “block” as used herein may be a portion, in particular a square or rectangular portion, of a picture. With reference, for example, to HEVC and VVC, the block may be or correspond to a CTU, a coding unit (CU), a prediction unit (PU), or a transform unit (TU) and/or to the corresponding blocks, e.g. a CTB, a coding block (CB), a transform block (TB) or a prediction block (PB).

For example, a CTU may be or comprise a CTB of luma samples and two corresponding CTBs of chroma samples of a picture that has three sample arrays, or a CTB of samples of a monochrome picture or a picture that is coded using three separate colour planes and syntax structures used to code the samples. Correspondingly, a CTB may be an N×N block of samples for some value of N, i.e. a square block, such that the division of a component into CTBs is a partitioning. A CU may be or comprise a coding block of luma samples and two corresponding coding blocks of chroma samples of a picture that has three sample arrays, or a coding block of samples of a monochrome picture or a picture that is coded using three separate color planes and syntax structures used to code the samples. Correspondingly, a CB may be an M×N block of samples for some values of M and N such that the division of a CTB into coding blocks is a partitioning.

In some embodiments, e.g., according to HEVC, a CTU may be split into CUs by using a quad-tree structure denoted as a coding tree. The decision whether to code a picture area using inter-picture (temporal) or intra-picture (spatial) prediction is made at the CU level. Each CU can be further split into one, two or four PUs according to the PU splitting type. Inside one PU, the same prediction process is applied and the relevant information is transmitted to the decoder on a PU basis. After obtaining the residual block by applying the prediction process based on the PU splitting type, a CU can be partitioned into transform units (TUs) according to another quad-tree structure similar to the coding tree for the CU.

In embodiments, e.g., according to the latest video coding standard currently in development, which is referred to as VVC, a combined QT and BT (QTBT) partitioning is for example used to partition a coding block. In the QTBT block structure, a CU can have either a square or rectangular shape. For example, a CTU is first partitioned by a quad-tree structure. The quad-tree leaf nodes are further partitioned by a BT or TT structure. The partitioning tree leaf nodes are called CUs, and that partition is used for prediction and transform processing without any further partitioning. This means that the CU, PU and TU have the same block size in the QTBT coding block structure. In parallel, multiple partitions, for example, triple-tree partition may be used together with the QTBT block structure.

In one example, the mode selection unit 260 of video encoder 20 may be configured to perform any combination of the partitioning techniques described herein.

As described above, the video encoder 20 is configured to determine or select the best or an optimum prediction mode from a set of (e.g. pre-determined) prediction modes. The set of prediction modes may comprise intra-prediction modes and/or inter-prediction modes.

Intra-Prediction

The set of intra-prediction modes may comprise 35 different intra-prediction modes, such as non-directional modes like direct current (DC) (or mean) mode and planar mode, or directional modes, e.g. as defined in HEVC, or may comprise 67 different intra-prediction modes, such as non-directional modes like DC (or mean) mode and planar mode, or directional modes, e.g. as defined for VVC.

The intra-prediction unit 254 is configured to use reconstructed samples of neighboring blocks of the same current picture to generate an (intra-)prediction block 265 according to an intra-prediction mode from the set of intra-prediction modes.

The intra-prediction unit 254 (or in general the mode selection unit 260) may be further configured to output intra-prediction parameters (or in general information indicative of the selected intra-prediction mode for the block) to the entropy encoding unit 270 in the form of syntax elements 266 for inclusion into the encoded picture data 21, so that, e.g., the video decoder 30 may receive and use the prediction parameters for decoding.

Inter-Prediction:

The set of (or possible) inter-prediction modes depends on the available reference pictures (i.e. previous, at least partially decoded pictures, e.g. stored in DBP 230) and other inter-prediction parameters, e.g. whether the whole reference picture or only a part, e.g. a search window area around the area of the current block, of the reference picture is used for searching for a best matching reference block, and/or e.g. whether pixel interpolation is applied, such as half/semi-pel and/or quarter-pel interpolation, or not.

In addition to the above prediction modes, skip mode and/or direct mode may be applied.

The inter-prediction unit 244 may include a motion estimation (ME) unit and a motion compensation (MC) unit (both not shown in FIG. 2). The motion estimation unit may be configured to receive or obtain the picture block 203 (current picture block 203 of the current picture 17) and a decoded picture 231, or at least one or a plurality of previously reconstructed blocks, such as reconstructed blocks of one or a plurality of previously decoded pictures 231, for motion estimation. By way of example, a video sequence may comprise the current picture and the previously decoded pictures 231, or in other words, the current picture and the previously decoded pictures 231 may be part of or form a sequence of pictures forming a video sequence.

The encoder 20 may be configured to select a reference block from a plurality of reference blocks of the same or different pictures of the plurality of previously decoded pictures and provide a reference picture (or reference picture index) and/or an offset (spatial offset) between the position (x, y coordinates) of the reference block and the position of the current block as inter-prediction parameters to the motion estimation unit. This offset is also called motion vector (MV).

The motion compensation unit may be configured to obtain, e.g. receive, an inter-prediction parameter and to perform inter-prediction based on or using the inter-prediction parameter to obtain an (inter-)prediction block 265. Motion compensation, performed by the motion compensation unit, may involve fetching or generating the prediction block based on the motion/block vector determined by motion estimation, possibly performing interpolations to sub-pixel precision. Interpolation filtering may generate additional pixel samples from known pixel samples, thus potentially increasing the number of candidate prediction blocks that may be used to code a picture block. Upon receiving the motion vector for the PU of the current picture block, the motion compensation unit may locate the prediction block to which the motion vector points in one of the reference picture lists.

The motion compensation unit may also generate syntax elements associated with the blocks and video slices for use by video decoder 30 in decoding the picture blocks of the video slice. In addition, or as an alternative to slices and respective syntax elements, tile groups and/or tiles and respective syntax elements may be generated or used.

MMVD:

MMVD, described as ultimate motion vector expression by S. Jeong et al. in “CE4 Ultimate motion vector expression (Test 4.5.4)”, document JVET-L0054, Joint Video Experts Team (WET) of ITU-T SG 16 WP 3 and International Organization for Standardization (ISO)/International Electrotechnical Commission (IEC) joint technical committee (JTC) 1/SC 29/WG 11, 12th Meeting: Macao, CN, 3-12 October 2018, is used for either skip or merge modes with a special motion vector expression method. MMVD re-uses merge candidates in the same way as in HEVC as described in HEVC, Rec. ITU-T H.265 and ISO/IEC 23008-2, December 2016. Among the merge candidates, a candidate may be selected, and is further expanded by a motion vector expression method. MMVD provides a new motion vector expression with simplified signaling. The expression method includes a starting point, a motion magnitude, and a motion direction. This technique uses a merge candidate list, but only candidates which are default merge type are considered for MMVD's expansion.

A base candidate index is used to define the starting point. The base candidate index may indicate the best candidate among the candidates in a candidate list as follows.

TABLE 1 Base candidate IDX Base candidate IDX 0 1 2 3 N^(th) MVP 1^(st) MVP 2^(nd) MVP 3^(rd) MVP 4^(th) MVP

If the number of base candidates in the list is equal to 1, the base candidate IDX is not signaled. A distance index is used as motion magnitude information. The distance index indicates a pre-defined distance from the starting point information. The pre-defined distances may be as follows:

TABLE 2 Distance IDX. Distance IDX 0 1 2 3 4 5 6 7 Pixel {square root over (1/4)}- {square root over (1/2)}- 1- 2- 4- 8- 16- 32- distance pel pel pel pel pel pel pel pel

The direction index represents the direction of the motion vector difference relative to the starting point. The direction index can represent one of the four directions as shown below.

TABLE 3 Direction IDX. Direction IDX 00 01 10 11 x-axis + − N/A N/A y-axis N/A N/A + −

Reordering MMVD's distance table:

The distance index table may be reordered according to the occurrence of usage of each distance index in previous coded pictures ranking from high to low, as for instance, described by J. Li, R.-L. Liao, and C. S. Lim in “CE4-related: Improvement on ultimate motion vector expression”, document JVET-L0408, JVET of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11 12th Meeting: Macao, CN, 03-12 October 2018. For example, assuming

Table 2 is used as the base distance table and 2-pel is used most often in a previous coded picture, the 2-pel distance will be assigned to index 0 instead of 3. The distance table is initialized before processing the picture. Initial table values may be loaded from the previous coded picture in reference picture list 0 with reference index 0.

Temporal layers:

Each access unit in HEVC as described by V. Sze, M. Budagavi, and G. J. Sullivan in the book “High Efficiency Video Coding (HEVC)”, ISSN 1558-9412 belongs to one temporal sub-layer, as indicated by the temporal identifier (ID). Since each access unit belongs to one temporal sub-layer, all video coding layer (VCL) network abstraction layer (NAL) units belonging to the same access unit must have the same temporal ID signaled in their NAL unit headers. HEVC prohibits the decoding process of pictures of any lower temporal sub-layer from having any dependencies on data sent for a higher temporal sub-layer. As shown in FIG. 2.3 of the above book, no pictures in the lower sub-layer reference any pictures in the higher sub-layer. Since there are no dependencies from higher sub-layers to lower sub-layers, it is possible to remove higher sub-layers from a bitstream to create a new bitstream with fewer pictures in it. The process of removing sub-layers is called sub-bitstream extraction, and the resulting bitstream is called a sub-bitstream of the original bitstream. Sub-bitstream extraction is done by discarding all NAL units which have a temporal ID higher than a target temporal ID value called HighestTid. HEVC encoders are required to ensure that each possible such sub-bitstream is itself a valid HEVC bitstream.

Entropy Coding:

The entropy encoding unit 270 is configured to apply, for example, an entropy encoding algorithm or scheme (e.g. a variable length coding (VLC) scheme, a context adaptive VLC scheme (CAVLC), an arithmetic coding scheme, a binarization, a context adaptive binary arithmetic coding (CABAC), syntax-based CABAC (SBAC), probability interval partitioning entropy (PIPE) coding or another entropy encoding methodology or technique) or bypass (no compression) on the quantized coefficients 209, inter-prediction parameters, intra-prediction parameters, loop filter parameters and/or other syntax elements to obtain encoded picture data 21 which can be output via the output 272, e.g. in the form of an encoded bitstream 21, so that, e.g., the video decoder 30 may receive and use the parameters for decoding. The encoded bitstream 21 may be transmitted to video decoder 30, or stored in a memory for later transmission or retrieval by video decoder 30.

Other structural variations of the video encoder 20 can be used to encode the video stream. For example, a non-transform based encoder 20 can quantize the residual signal directly without the transform processing unit 206 for certain blocks or frames. In another implementation, an encoder 20 can have the quantization unit 208 and the inverse quantization unit 210 combined into a single unit.

Decoder and Decoding Method:

FIG. 3 shows an example of a video decoder 30 that is configured to implement the techniques of the present application. The video decoder 30 is configured to receive encoded picture data 21 (e.g. encoded bitstream 21), e.g. encoded by encoder 20, to obtain a decoded picture 331. The encoded picture data or bitstream comprises information for decoding the encoded picture data, e.g. data that represents picture blocks of an encoded video slice (and/or tile group or tile) and associated syntax elements.

In the example of FIG. 3, the decoder 30 comprises an entropy decoding unit 304, an inverse quantization unit 310, an inverse transform processing unit 312, a reconstruction unit 314 (e.g. a summer 314), a loop filter 320, a DBP 330, a mode application unit 360, an inter-prediction unit 344 and an intra-prediction unit 354. Inter-prediction unit 344 may be or include a motion compensation unit. Video decoder 30 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder 20 of FIG. 2.

As explained with regard to the encoder 20, the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the loop filter 220, the DPB 230, the inter-prediction unit 244 and the intra-prediction unit 254 are also referred to as forming the “built-in decoder” of video encoder 20. Accordingly, the inverse quantization unit 310 may be identical in function to the inverse quantization unit 210, the inverse transform processing unit 312 may be identical in function to the inverse transform processing unit 212, the reconstruction unit 314 may be identical in function to reconstruction unit 214, the loop filter 320 may be identical in function to the loop filter 220, and the DPB 330 may be identical in function to the DPB 230. Therefore, the explanations provided for the respective units and functions of the video 20 encoder apply correspondingly to the respective units and functions of the video decoder 30.

Entropy Decoding:

The entropy decoding unit 304 is configured to parse the bitstream 21 (or in general encoded picture data 21) and perform, for example, entropy decoding to the encoded picture data 21 to obtain, e.g., quantized coefficients 309 and/or decoded coding parameters 366, such as any or all of inter-prediction parameters (e.g. reference picture index and motion vector), intra-prediction parameters (e.g. intra-prediction mode or index), transform parameters, QPs, loop filter parameters, and/or other syntax elements. Entropy decoding unit 304 may be configured to apply the decoding algorithms or schemes corresponding to the encoding schemes as described with regard to the entropy encoding unit 270 of the encoder 20. Entropy decoding unit 304 may be further configured to provide inter-prediction parameters, intra-prediction parameters and/or other syntax elements to the mode application unit 360 and other parameters to other units of the decoder 30. Video decoder 30 may receive the syntax elements at the video slice level and/or the video block level. In addition, or as an alternative to slices and respective syntax elements, tile groups and/or tiles and respective syntax elements may be received and/or used.

Inverse Quantization:

The inverse quantization unit 310 may be configured to receive QP (or in general, information related to the inverse quantization) and quantized coefficients from the encoded picture data 21 (e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304) and to apply, based on the QPs, an inverse quantization to the decoded quantized coefficients 309 to obtain dequantized coefficients 311, which may also be referred to as transform coefficients 311. The inverse quantization process may include use of a QP determined by video encoder 20 for each video block in the video slice (or tile or tile group) to determine a degree of quantization and, likewise, a degree of inverse quantization that should be applied.

Inverse Transform:

Inverse transform processing unit 312 may be configured to receive dequantized coefficients 311, also referred to as transform coefficients 311, and to apply a transform to the dequantized coefficients 311 in order to obtain reconstructed residual blocks 313 in the sample domain. The reconstructed residual blocks 313 may also be referred to as transform blocks 313. The transform may be an inverse transform, e.g., an inverse DCT, an inverse DST, an inverse integer transform, or a conceptually similar inverse transform process. The inverse transform processing unit 312 may be further configured to receive transform parameters or corresponding information from the encoded picture data 21 (e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304) to determine the transform to be applied to the dequantized coefficients 311.

Reconstruction:

The reconstruction unit 314 (e.g. adder or summer 314) may be configured to add the reconstructed residual block 313, to the prediction block 365 to obtain a reconstructed block 315 in the sample domain, e.g. by adding the sample values of the reconstructed residual block 313 and the sample values of the prediction block 365.

Filtering:

The loop filter unit 320 (either in the coding loop or after the coding loop) is configured to filter the reconstructed block 315 to obtain a filtered block 321, e.g. to smooth pixel transitions, or otherwise improve the video quality. The loop filter unit 320 may comprise one or more loop filters such as a de-blocking filter, a SAO filter or one or more other filters, e.g. a bilateral filter, an ALF, a sharpening, a smoothing filter or a collaborative filter, or any combination thereof. Although the loop filter unit 320 is shown in FIG. 3 as being an in-loop filter, in other configurations, the loop filter unit 320 may be implemented as a post loop filter.

DPB:

The decoded video blocks 321 of a picture are then stored in the DPB 330, which stores the decoded pictures 331 as reference pictures for subsequent motion compensation for other pictures and/or for output or respectively display.

The decoder 30 is configured to output the decoded picture 311, e.g. via output 312, for presentation or viewing to a user.

Prediction:

The inter-prediction unit 344 may be identical to the inter-prediction unit 244 (in particular, to the motion compensation unit) and the intra-prediction unit 354 may be identical to the intra-prediction unit 254 in function, and performs split or partitioning decisions and prediction based on the partitioning and/or prediction parameters or respective information received from the encoded picture data 21 (e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304). Mode application unit 360 may be configured to perform the prediction (intra- or inter-prediction) per block based on reconstructed pictures, blocks or respective samples (filtered or unfiltered) to obtain the prediction block 365.

When the video slice or picture is coded as an intra-coded (I) slice, intra-prediction unit 354 of mode application unit 360 is configured to generate prediction block 365 for a picture block of the current video slice based on a signaled intra-prediction mode and data from previously decoded blocks of the current picture. When the video slice or picture is coded as an inter-coded (i.e., B, or P) slice, inter-prediction unit 344 (e.g. motion compensation unit) of mode application unit 360 is configured to produce prediction block 365 for a video block of the current video slice based on the motion vectors and other syntax elements received from entropy decoding unit 304. For inter-prediction, the prediction blocks may be produced from one of the reference pictures within one of the reference picture lists. Video decoder 30 may construct the reference picture lists, List 0 and List 1, using default construction techniques based on reference pictures stored in DPB 330. The same or similar approach may be applied for or by embodiments using tile groups (e.g. video tile groups) and/or tiles (e.g. video tiles) in addition or alternatively to slices (e.g. video slices), e.g. a video may be coded using I, P or B tile groups and/or tiles.

Mode application unit 360 is configured to determine the prediction information for a video/picture block of the current (video) slice by parsing the motion vectors or related information and other syntax elements, and use the prediction information to produce the prediction block for the current video block being decoded. For example, the mode application unit 360 uses some of the received syntax elements to determine a prediction mode (e.g., intra- or inter-prediction) used to code the video blocks of the (video) slice, an inter-prediction slice type (e.g., B slice, P slice, or generalized PB (GPB) slice), construction information for one or more of the reference picture lists for the slice, motion vectors for each inter-coded video block of the slice, inter-prediction status for each inter-coded video block of the slice, and other information to decode the video blocks in the current (video) slice. The same or similar approach may be applied for or by embodiments using tile groups (e.g. video tile groups) and/or tiles (e.g. video tiles) in addition or alternatively to slices (e.g. (video) slices), e.g. a video may be coded using I, P or B tile groups and/or tiles.

Embodiments of the video decoder 30 as shown in FIG. 3 may be configured to partition and/or decode the picture by using slices (or as video slices), wherein a picture may be partitioned into or decoded using one or more slices (typically non-overlapping), and each slice may comprise one or more blocks (e.g. CTUs).

Embodiments of the video decoder 30 as shown in FIG. 3 may be configured to partition and/or decode the picture by using tile groups (or as video tile groups) and/or tiles (or as video tiles), wherein a picture may be partitioned into or decoded using one or more tile groups (typically non-overlapping), and each tile group may comprise one or more blocks (e.g. CTUs) or one or more tiles, wherein each tile may be of rectangular shape and may comprise one or more blocks (e.g. CTUs), e.g. complete or fractional blocks.

Other variations of the video decoder 30 can be used to decode the encoded picture data 21. For example, the decoder 30 can produce the output video stream without the loop filtering unit 320. For example, a non-transform based decoder 30 can inverse-quantize the residual signal directly without the inverse-transform processing unit 312 for certain blocks or frames. In another implementation, the video decoder 30 can have the inverse-quantization unit 310 and the inverse-transform processing unit 312 combined into a single unit.

It should be understood that, in the encoder 20 and the decoder 30, a processing result of a current step may be further processed and then output to the next step. For example, after interpolation filtering, motion vector derivation or loop filtering, a further operation, such as Clip or shift, may be performed on the processing result of the interpolation filtering, motion vector derivation or loop filtering.

It should be noted that further operations may be applied to the derived motion vectors of the current block (including but not limited to control point motion vectors of affine mode, sub-block motion vectors in affine, planar, advanced temporal motion vector prediction (ATMVP) modes, temporal motion vectors, and so on). For example, the value of a motion vector is constrained to a predefined range according to its representing bit number. If the representing bit number of the motion vector is bitDepth, then the range is −2{circumflex over ( )}(bitDepth-1)˜2(bitDepth-1)-1, where “{circumflex over ( )}” means exponentiation. For example, if bitDepth is set equal to 16, the range is −32768˜32767, if bitDepth is set equal to 18, the range is −131072˜131071. For example, the value of the derived motion vector (e.g. the MVs of four 4×4 sub-blocks within one 8×8 block) is constrained such that the maximum difference between integer parts of the four 4×4 sub-block MVs is no more than N pixels, such as no more than 1 pixel. The following description provides two methods for constraining the motion vector according to the bitDepth.

Method 1: remove the overflow most significant bit (MSB) by the following operations:

ux=(mvs+2^(bidDepth)) % ^(bitDepth),   (1)

mvx=(ux>=2^(bitDepth-1)) ? (ux−2^(bitDepth)): ux,   (2)

uy=(mvy+2^(bitDepth)) % 2^(bitDepth), and   (3)

mvy=(uy>=2^(bitDepth-1)) ? (uy−2^(bitDepth)): uy,   (4)

where mvx is a horizontal component of a motion vector of an image block or a sub-block, mvy is a vertical component of a motion vector of an image block or a sub-block, and ux and uy indicate respective intermediate values.

For example, if the value of mvx is −32769, after applying formulae (1) and (2), the resulting value is 32767. In a computer system, decimal numbers are stored as two's complements. The two's complement of −32769 is 1,0111,1111,1111,1111 (17 bits). Then, the MSB is discarded, so the resulting two's complement is 0111,1111,1111,1111 (decimal number is 32767), which is the same as the output by applying formulae (1) and (2).

ux=(mvpx+mvdx+2^(bitDepth)) % 2^(bitDepth),   (5)

mvx=(ux>=2^(bitDepht-1)) ? (ux−2^(bitDepth)): ux,   (6)

uy=(mvpy+mvdy+2^(bitDepth)) % 2^(bitDepth), and   (7)

mvy=(uy>=2^(bitDepth-1)) ? (uy−2^(bitDepth)): uy.   (8)

The operations may be applied during the sum of the MVP and the motion vector difference (mvd), as shown in formulae (5) to (8).

Method 2: remove the overflow MSB by clipping the value:

vx=Clip3(−2^(bitDepth-1), 2^(bitDepth-1)−1, vx), and

vy=Clip3(−2^(bitDepth-1), 2^(bitDepth-1)−1, vy),

where vx is a horizontal component of a motion vector of an image block or a sub-block, vy is a vertical component of a motion vector of an image block or a sub-block, x, y and z respectively correspond to three input values of the MV clipping process, and the definition of the function Clip3 is as follows:

${{Clip}\; 3\left( {x,y,z} \right)} = \left\{ \begin{matrix} x & ; & {z < x} \\ y & ; & {z > y} \\ z & ; & {otherwise} \end{matrix} \right.$

FIG. 4 is a schematic diagram of a video coding device 400 according to an embodiment of the present disclosure. The video coding device 400 is suitable for implementing the disclosed embodiments as described below. In an embodiment, the video coding device 400 may be a decoder such as video decoder 30 of FIG. 1A or an encoder such as video encoder 20 of FIG. 1A.

The video coding device 400 may comprise ingress ports 410 (or input ports 410) and a receiver unit (Rx) 420 for receiving data, a processor, logic unit, or central processing unit (CPU) 430 to process the data, a transmitter unit (Tx) 440 and egress ports 450 (or output ports 450) for transmitting the data, and a memory 460 for storing the data. The video coding device 400 may also comprise optical-to-electrical (OE) components and electrical-to-optical (EO) components coupled to the ingress ports 410, the receiver unit 420, the transmitter unit 440, and the egress ports 450 for egress or ingress of optical or electrical signals.

The processor 430 may be implemented by hardware and software. The processor 430 may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor), FPGAs, ASICs, and DSPs. The processor 430 may be in communication with the ingress ports 410, the receiver unit 420, the transmitter unit 440, egress ports 450, and the memory 460. The processor 430 may comprise a coding module 470. The coding module 470 implements the disclosed embodiments described above and below. For instance, the coding module 470 may implement, process, prepare, or provide the various coding operations. The inclusion of the coding module 470 therefore provides a substantial improvement to the functionality of the video coding device 400 and effects a transformation of the video coding device 400 to a different state. Alternatively, the coding module 470 may be implemented as instructions stored in the memory 460 and executed by the processor 430.

The memory 460 may comprise one or more disks, tape drives, and solid-state drives and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory 460 may be, for example, volatile and/or non-volatile and may be a read-only memory (ROM), RAM, ternary content-addressable memory (TCAM), and/or static RAM (SRAM).

FIG. 5 is a simplified block diagram of an apparatus 500 that may be used as either or both of the source device 12 and the destination device 14 from FIG. 1A according to an exemplary embodiment.

A processor 502 in the apparatus 500 can be a central processing unit. Alternatively, the processor 502 can be any other type of device, or multiple devices, capable of manipulating or processing information now-existing or hereafter developed. Although the disclosed implementations can be practiced with a single processor as shown, e.g., the processor 502, advantages in speed and efficiency can be achieved using more than one processor.

A memory 504 in the apparatus 500 can be a ROM device or a RAM device in an implementation. Any other suitable type of storage device can be used as the memory 504. The memory 504 can include code and data 506 that is accessed by the processor 502 using a bus 512. The memory 504 can further include an operating system 508 and application programs 510, the application programs 510 including at least one program that permits the processor 502 to perform the methods described herein. For example, the application programs 510 can include applications 1 through N, which further include a video coding application that performs the methods described herein.

The apparatus 500 can also include one or more output devices, such as a display 518. The display 518 may be, in one example, a touch sensitive display that combines a display with a touch sensitive element that is operable to sense touch inputs. The display 518 can be coupled to the processor 502 via the bus 512.

Although depicted here as a single bus, the bus 512 of the apparatus 500 can be composed of multiple buses. Further, a secondary storage (not shown) can be directly coupled to the other components of the apparatus 500 or can be accessed via a network and can comprise a single integrated unit such as a memory card or multiple units such as multiple memory cards. The apparatus 500 can thus be implemented in a wide variety of configurations.

Method of retrieving distance information from previously coded/decoded pictures.

In an example, an appropriate distance table of MMVD can increase the coding gain due to the ability of the encoder to get a desirable motion vector with a low index. To this end, a distance table may be provided where the most frequently used distances for the current picture are located at the beginning of the distance table. Some implementations can have more than one distance table, but their interaction should be the same as described below.

Embodiment 1

According to this embodiment, one or more distance tables are determined from a reference picture with a POC number that is closest to the POC number of the current picture or current processing unit. Furthermore, the one or more distance tables are obtained based on the number of MMVD blocks, i.e. blocks that are coded by the MMVD mode, in the reference picture.

In an example, the absolute differences between the POC number of the current picture and the POC numbers of the reference pictures (in an example, if a prediction mode of a reference picture is intra-prediction or if a reference picture is the current picture, this reference picture will not be used in the calculation) in the one or more reference lists are calculated. Hence, a set of absolute POC number differences is obtained. This set may comprise at least one absolute POC number difference. According to the smallest absolute difference in the set of absolute POC number differences, at least one reference picture with the closest POC number (corresponding to the smallest absolute difference) to the current picture is determined. At least one distance table is initialized based on the at least one reference picture with the closest POC number to the current picture, wherein intra frames and the current frame/picture are excluded.

If a quantity, i.e. number, of the reference pictures with the closest POC number is greater than 1, the at least one reference picture for initializing the at least one distance table is determined from the reference pictures with the closest POC number according to a quantity, i.e. number, of blocks with MMVD coding in the respective reference picture.

In one example, when there are two reference pictures (reference picture A and reference picture B) with the closest POC number, if a quantity of blocks with MMVD coding in reference picture A is greater than a quantity of blocks with MMVD coding in reference picture B, reference picture A is determined as the reference picture. If a quantity of blocks with MMVD coding in reference picture A is smaller than a quantity of blocks with MMVD coding in reference picture B, reference picture B is determined as the reference picture.

Furthermore, if there are several candidates, i.e. reference pictures, having an equal number of blocks with MMVD coding (for example, a quantity of blocks with MMVD coding in reference picture A is equal to a quantity of blocks with MMVD coding in reference picture B), the reference picture in the reference picture list with lower list number, i.e. reference picture list index, is used (for example, if reference picture A is in reference picture list 0, and reference picture B is in reference picture list 1, reference picture A is determined as the reference picture).

If there are several candidates having an equal number of blocks with MMVD coding which are located in the same reference picture list (for example, a quantity of blocks with MMVD coding in reference picture A is equal to a quantity of blocks with MMVD coding in reference picture B, and both, reference picture A and reference picture B are in reference picture list 0, or both, reference picture A and reference picture B are in reference picture list 1), the one that has the lower reference picture index is used (for example, if a reference picture index corresponding to reference picture A is smaller than a reference picture index corresponding to reference picture B, reference picture A is determined as the reference picture, or if a reference picture index corresponding to reference picture A is greater than a reference picture index corresponding to reference picture B, reference picture B is determined as the reference picture).

At least one distance table is retrieved from this reference picture and used for the current picture. If no suitable reference picture has been found (in an example, if a prediction mode of the reference picture with the closest POC number is intra-prediction or if it is the current picture, then there is no suitable reference picture), values in the corresponding default distance table, for example, the values in

Table 2, are used for the current picture. After processing the current picture, statistics of usage of each index in the at least one distance table are collected and the values corresponding to the indices are rearranged in the at least one distance table, for example, according to their frequency of occurrence. In a further example, the number of used MMVD blocks is collected and saved with relation to the current picture.

Using reference pictures with the closest POC number exploits the temporal correlation between the current picture and the reference picture. A large number of blocks with MMVD coding improves the significance of the statistics for re-ordering the distance table. A lower reference picture list index prefers a forward prediction of the prediction block. A lower reference picture index reduces the signaling amount.

Embodiment 2

According to this embodiment, one or more distance tables are determined from a reference picture with a POC number that is closest to the POC number of the current picture. Furthermore, the one or more distance tables are obtained based on the number of square MMVD blocks in the reference picture. Instead of the number of square MMVD blocks, the total area, i.e. number of samples, coded by MMVD coding may be used as the parameter of the reference picture.

In an example, the absolute differences between the POC number of the current picture and the POC numbers of the reference pictures (in an example, if a prediction mode of a reference picture is intra-prediction or if a reference picture is the current picture, this reference picture will not be used in the calculation) in the one or more reference lists are calculated. Hence, a set of absolute POC number differences is obtained. This set may comprise at least one absolute POC number difference. According to the smallest absolute difference in the set of absolute POC number differences, at least one reference picture with the closest POC number (corresponding to the smallest absolute difference) to the current picture is determined. At least one distance table is initialized based on the at least one reference picture with the closest POC number to the current picture. In particular, all entries in the one or more reference lists with POC numbers closest to the POC number of the current picture are found, wherein intra frames and current frame/picture are excluded.

If a quantity, i.e. number, of the reference pictures with the closest POC number is greater than 1, the at least one reference picture for initializing the at least one distance table is determined from the reference pictures with the closest POC number according to a quantity, i.e. number, of blocks with MMVD coding in the respective reference picture.

In one example, when there are two reference pictures (reference picture A and reference picture B) with the closest POC number, if a quantity of square blocks with MMVD coding in reference picture A is greater than a quantity of square blocks with MMVD coding in reference picture B, reference picture A is determined as the reference picture. If a quantity of square blocks with MMVD coding in reference picture A is smaller than a quantity of square blocks with MMVD coding in reference picture B, reference picture B is determined as the reference picture.

If there are several candidates, i.e. reference pictures, having an equal number of square blocks with MMVD coding (for example, a quantity of square blocks with MMVD coding in reference picture A is equal to a quantity of square blocks with MMVD coding in reference picture B), the reference picture in the reference picture list with lower list number, i.e. reference picture list index, is used (for example, if reference picture A is in reference picture list 0 and reference picture B is in reference picture list 1, reference picture A is determined as the reference picture).

If there are several candidates having an equal number of square blocks with MMVD coding which are located in the same reference picture list (for example, a quantity of square blocks with MMVD coding in reference picture A is equal to a quantity of square blocks with MMVD coding in reference picture B, and both, reference picture A and reference picture B are in reference picture list 0, or both, reference picture A and reference picture B are in reference picture list 1), the one that has the lower reference picture index is used (for example, if a reference picture index corresponding to reference picture A is smaller than a reference picture index corresponding to reference picture B, reference picture A is determined as the reference picture, or if a reference picture index corresponding to reference picture A is greater than a reference picture index corresponding to reference picture B, reference picture B is determined as the reference picture).

At least one distance table is retrieved from this reference picture and used for the current picture. If no suitable reference picture has been found (in an example, if a prediction mode of the reference picture with the closest POC number is intra-prediction or if it is the current picture, then there is no suitable reference picture), values in the corresponding default distance table, for example, the values in

Table 2, are used for the current picture. After processing the current picture, statistics of usage of each index in the at least one distance table are collected and the values corresponding to the indices are rearranged, for example, according to their frequency of occurrence. In a further example, the number of used square MMVD blocks is collected and saved with relation to the current picture.

Using reference pictures with the closest POC number exploits the temporal correlation between the current picture and the reference picture. A large number of square blocks with MMVD coding improves the significance of the statistics for re-ordering the distance table. A lower reference picture list index prefers a forward prediction of the prediction block. A lower reference picture index reduces the signaling amount.

Embodiment 3

According to this embodiment, one or more distance tables are determined from a reference picture with a POC number that is closest to the POC number of the current picture and with a smaller QP.

In an example, the at least one distance table is initialized based on at least one reference picture with the closest POC number to the current picture (In some examples, this step is the same as in the above-described embodiments 1 and 2). In particular, all entries in the one or more reference lists with POC numbers closest to the POC number of the current picture are found, wherein intra frames and the current frame/picture are excluded.

If there are several reference pictures having the closest POC number, one or more candidates/reference pictures which have the smaller QP are used (for example, if the QP of reference picture A is smaller than the QP of reference picture B, reference picture A is determined as the reference picture). If there are several candidates having equal QP (in an example, the QP of reference picture A is equal to the QP of reference picture B), the reference picture in the reference picture list with lower list number, i.e. reference picture list index, is used (for example, if reference picture A is in reference picture list 0 and reference picture B is in reference picture list 1, reference picture A is determined as the reference picture).

If there are several candidates having equal QP which are located in the same reference picture list (for example, the QP of reference picture A is equal to the QP of reference picture B, and both, reference picture A and reference picture B are in reference picture list 0, or both, reference picture A and reference picture B are in reference picture list 1), the one that has lower reference picture index is used (for example, if a reference picture index corresponding to reference picture A is smaller than a reference picture index corresponding to reference picture B, reference picture A is determined as the reference picture, or if a reference picture index corresponding to reference picture A is greater than a reference picture index corresponding to reference picture B, reference picture B is determined as the reference picture).

At least one distance table is retrieved from this picture and used for the current picture. If no suitable reference picture has been found (in an example, if a prediction mode of the reference picture with the closest POC number is intra-prediction or if it is the current picture, then there is no suitable reference picture), values in the corresponding default distance table, for example, the values in

Table 2, are used for the current picture. After processing the current picture, statistics of usage of each index in the at least one distance table are collected and the values corresponding to the indices are rearranged, for example, according to their frequency of occurrence.

Using reference pictures with the closest POC number exploits the temporal correlation between the current picture and the reference picture. A smaller QP reduces the losses during quantization due to a smaller quantization step size. A lower reference picture list index prefers a forward prediction of the prediction block. A lower reference picture index reduces the signaling amount.

FIG. 6 shows a flow chart illustrating the methods of determining a distance table of an MMVD mode according to embodiments 1 to 3. In a first step 610, a reference picture is determined from at least one reference picture list of a current processing unit based on at least one parameter of the reference picture, wherein the at least one parameter of the reference picture is selected from a group consisting of a POC number of the reference picture, a number of MMVD blocks of the reference picture, a reference picture list index of the reference picture, a reference picture index of the reference picture, and a QP of the reference picture.

In detail, at least one candidate reference picture with a POC number closest to a POC number of the current processing unit is obtained, wherein the reference picture is determined from the at least one candidate reference picture. If there are several candidate reference pictures, a subset of at least one candidate reference picture is selected based on one of the largest number of MMVD blocks, the largest number of square MMVD blocks, and the smallest QP. If there are still several candidate reference pictures, a further subset of at least one candidate reference picture is selected based on the lowest reference picture list index. If there still remains more than one candidate reference picture, that candidate reference picture with the lowest reference picture index is selected as the reference picture for the distance table.

Finally, the distance table is obtained for the current processing unit based on the selected reference picture in step 620.

Embodiment 4

According to this embodiment, one or more distance tables are determined from a reference picture with a QP closest to the QP of the current picture.

In an example, the at least one distance table is initialized based on at least one reference picture with the closest QP to the current picture, i.e. with the smallest absolute QP difference to the current picture (In some examples, this step is similar to the processes in the above-described embodiments 1 and 2 to obtain the reference picture with the closest POC number). In particular, all entries in the one or more reference lists with QPs closest to the QP of the current picture are found, wherein intra frames and the current frame/picture are excluded.

If there are several reference pictures having the smallest absolute QP difference, one or more candidates/reference pictures which have the smaller QP are used (for example, if the QP of reference picture A is smaller than the QP of reference picture B, reference picture A is determined as the reference picture). If there are several candidates having equal QP (in an example, the QP of reference picture A is equal to the QP of reference picture B), the reference picture in the reference picture list with lower list number, i.e. reference picture list index, is used (for example, if reference picture A is in reference picture list 0 and reference picture B is in reference picture list 1, reference picture A is determined as the reference picture).

If there are several candidates having equal QP which are located in the same reference picture list (for example, the QP of reference picture A is equal to the QP of reference picture B, and both, reference picture A and reference picture B are in reference picture list 0, or both, reference picture A and reference picture B are in reference picture list 1), the one that has the lower reference picture index is used (for example, if a reference picture index corresponding to reference picture A is smaller than a reference picture index corresponding to reference picture B, reference picture A is determined as the reference picture, or if a reference picture index corresponding to reference picture A is greater than a reference picture index corresponding to reference picture B, reference picture B is determined as the reference picture).

At least one distance table is retrieved from this picture and used for the current picture. If no suitable reference picture has been found (in an example, if a prediction mode of the reference picture with the closest QP is intra-prediction or if it is the current picture, then there is no suitable reference picture), values in the corresponding default distance table, for example, the values in

Table 2, are used for the current picture. After processing the current picture, statistics of usage of each index in the at least one distance table are collected and the values corresponding to the indices are rearranged, for example, according to their frequency of occurrence.

Using reference pictures with a smaller QP reduces the losses during quantization due to a smaller quantization step size. A lower reference picture list index prefers a forward prediction of the prediction block. A lower reference picture index reduces the signaling amount.

FIG. 7 shows a flow chart illustrating the method of determining a distance table of an MMVD mode according to embodiment 4. In a first step 710, a reference picture is determined from at least one reference picture list of a current processing unit based on at least one parameter of the reference picture, wherein the at least one parameter of the reference picture is selected from a group consisting of a POC number of the reference picture, a number of MMVD blocks of the reference picture, a reference picture list index of the reference picture, a reference picture index of the reference picture, and a QP of the reference picture.

In detail, at least one candidate reference picture with a smallest absolute QP difference to the current processing unit is obtained, wherein the reference picture is determined from the at least one candidate reference picture. If there are several candidate reference pictures, a subset of at least one candidate reference picture is selected based on the smallest QP. If there are still several candidate reference pictures, a further subset of at least one candidate reference picture is selected based on the lowest reference picture list index. If there still remains more than one candidate reference picture, that candidate reference picture with the lowest reference picture index is selected as the reference picture for the distance table.

Finally, the distance table is obtained for the current processing unit based on the selected reference picture in step 720.

Embodiment 5

According to this embodiment, one or more distance tables are determined from a reference picture referred to by an MMVD MVP.

In an example, the at least one distance table is retrieved from a reference picture that is referred to by the reference picture index of the selected MVP candidate of the current block. In the case of a uni-predictive motion vector, only one reference picture is selected. In the case of a bi-predictive motion vector, it is possible to have two different reference pictures. A method of the selecting the reference picture for retrieving the at least one distance table from several candidate reference pictures can be one of those described above.

Embodiment 6

According to this embodiment, one or more distance tables are stored between frames in decoding order.

In one example, it is proposed to use one or more distance tables from the previous picture (or frame) in the same temporal layer in decoding order. The decoder may store a set of distance tables for every temporal layer. In an example, for an intra random access pictures (TRAP) frame, all TRAP frames may be reset to a default distance table, where

Table 2 shows an example. At the beginning of processing the current picture, the decoder may use at least one distance table from the set of distance tables stored for the corresponding temporal layer. After processing the picture and collecting statistics of using entries of the at least one distance table, a new distance table may be determined and stored in the set of distance tables of the corresponding layer and optionally for the higher temporal layer too.

Embodiment 7

According to this embodiment, the at least one distance table is explicitly signaled.

In this embodiment, it is proposed to explicitly signal the at least one distance table on the frame level. Every entry of the distance table is converted to its index, for example as shown in

Table 2, and encoded by one of the following: coded by fixed code or coded by delta-coded modulation.

Embodiment 8

According to this embodiment, the at least one distance table is rearranged during processing of the frame/picture.

In an example, the at least one distance table is modified during the processing of the picture (or frame) e.g. by rearranging of entries of the at least one distance table, by replacing, adding or removing entries. Every tile and/or slice in a picture may have its own at least one distance table, that is initialized at the beginning of the processing. A method of getting the initial values of the at least one distance table can be according to any one of the above-described embodiments and examples.

The initial values are copied to the at least one distance table of the respective tile or slice. During processing of the tile or slice, at least one distance table is reordered, for example based on statistics of selecting entries from at least one distance table for the previous coding units in the same tile or slice and a gain of a motion vector difference in advanced motion vector prediction (AMVP). During processing of the tile or slice, statistics of usage of MMVD blocks and/or square MMVD blocks and/or total area of MMVD blocks are collected. After processing the picture, the at least one distance table from one of the tiles or slices with the largest number of used MMVD blocks is saved in relation to the current picture. If several tiles or slices have the same number of MMVD blocks, the at least one distance table from the tile or slice that is closest to the center of the picture is used. If several tiles or slices are equally close to the center, the at least one distance table from the tile or slice with higher number of square MMVD blocks or higher total area of MMVD blocks is used. If several tiles or slices are equally close to the center and have the same number of square MMVD blocks, the at least one distance table from the tile or slice that is closest to the top-left corner of the picture is used.

Mathematical Operators:

The mathematical operators used in this application are similar to those used in the C programming language. However, the results of integer division and arithmetic shift operations are defined more precisely, and additional operations are defined, such as exponentiation and real-valued division. Numbering and counting conventions generally begin from 0, i.e. “the first” is equivalent to the 0-th, “the second” is equivalent to the 1st, etc.

Arithmetic Operators

The following arithmetic operators are defined as follows:

TABLE 4 Arithmetic operators + Addition − Subtraction (as a two-argument operator) or negation (as a unary prefix operator) * Multiplication, including matrix multiplication x^(y) Exponentiation. Specifies x to the power of y. In other contexts, such notation is used for superscripting not intended for interpretation as exponentiation. / Integer division with truncation of the result toward zero. For example, 7/4 and −7/−4 are truncated to 1 and −7/4 and 7/−4 are truncated to −1. ÷ Used to denote division in mathematical equations where no truncation or rounding is intended. $\frac{x}{y}$ Used to denote division in mathematical equations where no truncation or rounding is intended. $\sum\limits_{i = x}^{y}{f(i)}$ The summation of f(i) with i taking all integer values from x up to and including y. x % y Modulus. Remainder of x divided by y, defined only for integers x and y with x >= 0 and y > 0.

Logical Operators:

The following logical operators are defined as follows:

x && y Boolean logical “and” of x and y

x| |y Boolean logical “or” of x and y

Boolean logical “not”

x ? y:z If x is TRUE or not equal to 0, evaluates to the value of y; otherwise, evaluates to the value of z.

Relational operators:

The following relational operators are defined as follows:

>Greater than

>=Greater than or equal to

<Less than

<=Less than or equal to

==Equal to

!=Not equal to

When a relational operator is applied to a syntax element or variable that has been assigned the value “na” (not applicable), the value “na” is treated as a distinct value for the syntax element or variable. The value “na” is considered not to be equal to any other value.

Bit-wise Operators:

The following bit-wise operators are defined as follows:

-   -   & Bit-wise “and”. When operating on integer arguments, operates         on a two's complement representation of the integer value. When         operating on a binary argument that contains fewer bits than         another argument, the shorter argument is extended by adding         more significant bits equal to 0.     -   | Bit-wise “or”. When operating on integer arguments, operates         on a two's complement representation of the integer value. When         operating on a binary argument that contains fewer bits than         another argument, the shorter argument is extended by adding         more significant bits equal to 0.     -   {circumflex over (′)} Bit-wise “exclusive or”. When operating on         integer arguments, operates on a two's complement representation         of the integer value. When operating on a binary argument that         contains fewer bits than another argument, the shorter argument         is extended by adding more significant bits equal to 0.     -   x >>y Arithmetic right shift of a two's complement integer         representation of x by y binary digits. This function is defined         only for non-negative integer values of y. Bits shifted into the         most significant bits (MSBs) as a result of the right shift have         a value equal to the MSB of x prior to the shift operation.     -   x <<y Arithmetic left shift of a two's complement integer         representation of x by y binary digits. This function is defined         only for non-negative integer values of y. Bits shifted into the         least significant bits (LSBs) as a result of the left shift have         a value equal to 0.

Assignment Operators:

The following arithmetic operators are defined as follows:

-   -   = Assignment operator     -   ++ Increment, i.e., x++ is equivalent to x=x+1; when used in an         array index, evaluates to the value of the variable prior to the         increment operation.     -   −− Decrement, i.e., x−− is equivalent to x=x−1; when used in an         array index, evaluates to the value of the variable prior to the         decrement operation.     -   += Increment by amount specified, i.e., x+=3 is equivalent to         x=x+3, and     -   x+=(−3) is equivalent to x=x+(−3).     -   −= Decrement by amount specified, i.e., x−=3 is equivalent to         x=x−3, and     -   x−=(−3) is equivalent to x=x−(−3).

Range Notation:

The following notation is used to specify a range of values:

-   -   x=y..z x takes on integer values starting from y to z,         inclusive, with x, y, and z being integer numbers and z being         greater than y.

Mathematical Functions:

The following mathematical functions are defined:

${{Abs}(x)} = \left\{ \begin{matrix} x & ; & {x>=0} \\ {- x} & ; & {x < 0} \end{matrix} \right.$

-   -   Asin(x) the trigonometric inverse sine function, operating on an         argument x that is in the range of −1.0 to 1.0, inclusive, with         an output value in the range of −π÷2 to π÷2, inclusive, in units         of radians.     -   Atan(x) the trigonometric inverse tangent function, operating on         an argument x, with an output value in the range of −π÷2 to π÷2,         inclusive, in units of radians.

${A\tan 2\left( {y,x} \right)} = \left\{ \begin{matrix} {A\;{\tan\left( \frac{y}{x} \right)}} & ; & {x > 0} \\ {{A\;{\tan\left( \frac{y}{x} \right)}} + \pi} & ; & {{x < 0}\&\&{y>=0}} \\ {{A\;{\tan\left( \frac{y}{x} \right)}} - \pi} & ; & {{x < 0}\&\&{y < 0}} \\ {+ \frac{\pi}{2}} & ; & {{x==0}\&\&{y>=0}} \\ {- \frac{\pi}{2}} & ; & {otherwise} \end{matrix} \right.$

-   -   Ceil(x) the smallest integer greater than or equal to x.

Clip 1_(Y)(x) = Clip 3(0, (1 ⪡ BitDepth_(Y)) − 1, x) Clip 1_(C)(x) = Clip 3(0, (1 ⪡ BitDepth_(C)) − 1, x) ${{Clip}\; 3\left( {x,y,z} \right)} = \left\{ \begin{matrix} x & ; & {z < x} \\ y & ; & {z > y} \\ z & ; & {otherwise} \end{matrix} \right.$

-   -   Cos(x) the trigonometric cosine function operating on an         argument x in units of radians.     -   Floor(x) the largest integer less than or equal to x.

${{GetCurrMsb}\left( {a,b,c,d} \right)} = \left\{ \begin{matrix} {c + d} & ; & {{b - a}\ >={d/2}} \\ {c - d} & ; & {{a - b}\  > {d/2}} \\ c & ; & {otherwise} \end{matrix} \right.$

-   -   Ln(x) the natural logarithm of x (the base-e logarithm, where e         is the natural logarithm base constant 2.718 281 828 . . . ).     -   Log 2(x) the base-2 logarithm of x.     -   Log 10(x) the base-10 logarithm of x.

${{Min}\left( {x,y} \right)} = \left\{ {{\begin{matrix} x & ; & {x<=y} \\ y & ; & {x > y} \end{matrix}{{Max}\left( {x,y} \right)}} = \left\{ {{\begin{matrix} x & ; & {x>=y} \\ y & ; & {x < y} \end{matrix}{Round}\mspace{14mu}(x)} = {{{Sign}\mspace{14mu}(x)*{Floor}\mspace{14mu}\left( {{{Abs}(x)} + 0.5} \right){Sign}\mspace{14mu}(x)} = \left\{ \begin{matrix} 1 & ; & {x > 0} \\ 0 & ; & {x==0} \\ {- 1} & ; & {x < 0} \end{matrix} \right.}} \right.} \right.$

-   -   Sin(x) the trigonometric sine function operating on an argument         x in units of radians     -   Sqrt(x)=√{square root over (x)}     -   Swap(x, y)=(y, x)     -   Tan(x) the trigonometric tangent function operating on an         argument x in units of radians

Order of Operation Precedence:

When an order of precedence in an expression is not indicated explicitly by use of parentheses, the following rules apply:

Operations of a higher precedence are evaluated before any operation of a lower precedence.

Operations of the same precedence are evaluated sequentially from left to right.

The table below specifies the precedence of operations from highest to lowest; a higher position in the table indicates a higher precedence.

For those operators that are also used in the C programming language, the order of precedence used in this Specification is the same as used in the C programming language.

TABLE 5 Operation precedence from highest (at top of table) to lowest (at bottom of table) operations (with operands x, y, and z) ″x++″, ″x−−″ ″!x″, ″−x″ (as a unary prefix operator) x^(y) ${{\,^{''}x}*y^{''}},{{\,^{''}x}\text{/}y^{''}},{{\,^{''}x} \div y^{''}},{{\,^{''}\frac{x}{y}}\,^{''}},{{\,^{''}x}\mspace{14mu}\%\mspace{14mu} y^{''}}$ ″x + y″, ″x − y″ (as a two-argument operator), $\;^{''}{\sum\limits_{i = x}^{y}\;{{f(i)}\mspace{11mu}\,^{''}}}$ ″x << y″, ″x >> y″ ″x < y″, ″x <= y″, ″x > y″, ″ x >= y″ ″x = = y″, ″x != y″ ″x & y″ ″x|y″ ″x && y″ ″x∥y″ ″x ? y : z″ ″x . . . y″ ″x = y″, ″x += y″, ″x −= y″

Text Description of Logical Operations

In the text, a statement of logical operations as would be described mathematically in the following form:

  if( condition 0 )  statement 0 else if( condition 1 )  statement 1 . . . else /* informative remark on remaining condition */  statement n may be described in the following manner: . . . as follows / . . . the following applies: If condition 0, statement 0 Otherwise, if condition 1, statement 1

Otherwise (informative remark on remaining condition), statement n

Each “If . . . Otherwise, if . . . Otherwise, . . . ” statement in the text is introduced with “. . . as follows” or “. . . the following applies” immediately followed by “If . . . ”. The last condition of the “If . . . Otherwise, if . . . Otherwise, . . . ” is always an “Otherwise, . . . ”. Interleaved “If . . . Otherwise, if . . . Otherwise, . . . ” statements can be identified by matching “. . . as follows” or “. . . the following applies” with the ending “Otherwise, . . . ”.

In the text, a statement of logical operations as would be described mathematically in the following form:

if( condition 0a && condition 0b )  statement 0 else if( condition 1a | | condition 1b )  statement 1 . . . else  statement n may be described in the following manner:    . . . as follows / . . . the following applies: If all of the following conditions are true, statement 0:   condition 0a   condition 0b Otherwise, if one or more of the following conditions are true, statement 1:   condition 1a   condition 1b . . . Otherwise, statement n

In the text, a statement of logical operations as would be described mathematically in the following form:

  if( condition 0 )  statement 0 if( condition 1 )  statement 1   may be described in the following manner:   When condition 0, statement 0   When condition 1, statement 1

Although embodiments of the disclosure, have been primarily described based on video coding, it should be noted that embodiments of the coding system 10, encoder 20 and decoder 30 (and correspondingly the system 10) and the other embodiments described herein may also be configured for still picture processing or coding, i.e. the processing or coding of an individual picture independent of any preceding or consecutive picture as in video coding. In general only inter-prediction units 244 (encoder) and 344 (decoder) may not be available in case the picture processing coding is limited to a single picture 17. All other functionalities (or as tools or technologies) of the video encoder 20 and the video decoder 30 may equally be used for still picture processing, e.g. residual calculation 204/304, transform 206, quantization 208, inverse quantization 210/310, (inverse) transform 212/312, partitioning 262, intra-prediction 254/354, and/or loop filtering 220, 320, and entropy coding 270 and entropy decoding 304.

Embodiments, e.g. of the encoder 20 and the decoder 30, and functions described herein, e.g. with reference to the encoder 20 and the decoder 30, may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on a computer-readable medium or transmitted over communication media as one or more instructions or code and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which correspond to tangible media such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which are non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

By way of example, and not limiting, such computer-readable storage media can comprise RAM, ROM, electrically erasable programmable ROM (EEPROM), compact disc (CD) ROM (CD-ROM) or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, include compact disc (CD), laser disc, optical disc, DVD, floppy disk and BLU-RAY DISC, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one or more DSPs, general purpose microprocessors, ASICs, FPGAs, or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware. 

1. A method comprising: determining a reference picture from a reference picture list of a current processing unit based on a parameter of the reference picture, wherein the parameter comprises one of a first picture order count (POC) number of the reference picture, a number of merge with motion vector difference (MMVD) blocks of the reference picture, a reference picture list index of the reference picture, a reference picture index of the reference picture, or a quantization parameter (QP) of the reference picture; and obtaining a distance table of an MMVD mode for the current processing unit based on the reference picture.
 2. The method of claim 1, further comprising: obtaining a first candidate reference picture comprising a second POC number closest to a third POC number of the current processing unit, wherein the reference picture is the first candidate reference picture; obtaining a second candidate reference picture comprising a smallest absolute QP difference to the current processing unit, wherein the reference picture is the second candidate reference picture; obtaining a third candidate reference picture comprising a smallest QP, wherein the reference picture is the candidate reference picture; obtaining a fourth candidate reference picture comprising a largest number of MMVD blocks, wherein the reference picture is the fourth candidate reference picture; obtaining a fifth candidate reference picture comprising a lowest reference picture list index, wherein the reference picture is the fifth candidate reference picture; or obtaining a sixth candidate reference picture comprising a lowest reference picture index, wherein the reference picture is the sixth candidate reference picture.
 3. The method of claim 1, wherein the reference picture satisfies one of the following conditions: the reference picture has a second POC number closest to a third POC number of the current processing unit among reference pictures of the reference picture list; the reference picture has a smallest absolute QP difference to the current processing unit among the reference pictures; the reference picture has a same reference picture list index as a motion vector predictor, (MVP) of a current block in the current processing unit; the reference picture has a same reference picture index as the MVP; the reference picture has a largest number of MMVD blocks among the reference pictures; the reference picture has a smallest QP among the reference pictures; the reference picture has a lowest reference picture list index among the reference pictures; or the reference picture has a lowest reference picture index among the reference pictures.
 4. The method of claim 1, further comprising obtaining a default distance table for the current processing unit when the reference picture is an intra frame.
 5. The method of claim 1, further comprising retrieving a distance table for the reference picture as the distance table for the current processing unit.
 6. The method of claim 1, wherein the current processing unit is a picture, a tile, or a slice.
 7. The method of claim 1, wherein the number of MMVD blocks is either a quantity of blocks coded by the MMVD mode or a quantity of square blocks coded by the MMVD mode.
 8. The method of claim 1, wherein the distance table represents a relationship between an absolute value of a motion vector difference and a distance index, and wherein information of the distance index is carried by a bitstream.
 9. An apparatus comprising: a memory configured to store instructions; and a processor in communication with the memory, wherein the instructions cause the processor to be configured to: determine a reference picture from a reference picture list of a current processing unit based on a parameter of the reference picture, wherein the parameter comprises one of a first picture order count (POC) number of the reference picture, a number of merge with motion vector difference (MMVD) blocks of the reference picture, a reference picture list index of the reference picture, a reference picture index of the reference picture, and a quantization parameter (QP) of the reference picture; and obtain a distance table of an MMVD mode for the current processing unit based on the reference picture.
 10. The apparatus of claim 9, wherein the instructions further cause the processor to be configured to: obtain a first candidate reference picture comprising a second POC number closest to a third POC number of the current processing unit, wherein the reference picture is the first candidate reference picture; obtain a second candidate reference picture comprising a smallest absolute QP difference to the current processing unit, wherein the reference picture is the second candidate reference picture; obtain a third candidate reference picture comprising a smallest QP, wherein the reference picture is the third candidate reference picture; obtain a fourth candidate reference picture comprising a largest number of MMVD blocks, wherein the reference picture is the fourth candidate reference picture; or obtain a sixth candidate reference picture comprising a lowest reference picture list index, wherein the reference picture is the fifth candidate reference picture; or obtain a sixth candidate reference picture comprising a lowest reference picture index, wherein the reference picture is the sixth candidate reference picture.
 11. The apparatus of claim 9, wherein the reference picture satisfies one of the following conditions: the reference picture has a second POC number closest to a third POC number of the current processing unit among the reference pictures of the reference picture list; the reference picture has a smallest absolute QP difference to the current processing unit among the reference pictures; the reference picture has a same reference picture list index as a motion vector predictor, (MVP) of a current block in the current processing unit; the reference picture has a same reference picture index as the MVP; the reference picture has a largest number of MMVD blocks among the reference pictures 4; the reference picture has a smallest QP among the reference pictures; the reference picture has a lowest reference picture list index among the reference pictures; the reference picture has a lowest reference picture index among the reference pictures.
 12. The apparatus of claim 9, wherein the instructions further cause the processor to be configured to obtain a default distance table for the current processing unit when the reference picture is an intra frame.
 13. The apparatus of claim 9, wherein the instructions further cause the processor to be configured to retrieve a distance table for the reference picture as the distance table for the current processing unit.
 14. The apparatus of claim 9, wherein the current processing unit is a picture, or a tile, or a slice.
 15. The apparatus of claim 9, wherein the number of MMVD blocks is either a quantity of blocks coded by the MMVD mode or a quantity of square blocks coded by the MMVD mode.
 16. The apparatus of claim 9, wherein the distance table represents a relationship between an absolute value of a motion vector difference and a distance index, and wherein information of the distance index is carried by a bitstream.
 17. A computer program product comprising computer-executable instructions, for performing linear predictive coding (LPC) of an audio signal, stored on a non-transitory computer-readable medium that, when executed by a processor, cause an apparatus to: detertnine a reference picture from a reference picture list of a current processing unit based on a parameter of the reference picture, wherein the parameter comprises one of a first picture order count (POC) number of the reference picture, a number of merge with motion vector difference (MMVD) blocks of the reference picture, a reference picture list index of the reference picture, a reference picture index of the reference picture, or a quantization parameter (QP) of the reference picture; and obtain a distance table of an MMVD mode for the current processing unit based on the reference picture.
 18. The computer program product of claim 17, wherein the computer-executable instructions further cause the apparatus to: obtain a first candidate reference picture comprising a second POC number closest to a third POC number of the current processing unit, wherein the reference picture is the first candidate reference picture; one obtain a second candidate reference picture comprising a smallest absolute QP difference to the current processing unit, wherein the reference picture is the second candidate reference picture; obtain a third candidate reference picture comprising a smallest QP, wherein the reference picture is the third candidate reference picture; obtain a fourth candidate reference picture comprising a largest number of MMVD blocks, wherein the reference picture is the fourth candidate reference picture; obtain a fifth candidate reference picture comprising a lowest reference picture list index, wherein the reference picture is the fifth candidate reference picture; or obtain a sixth candidate reference picture comprising a lowest reference picture index, wherein the reference picture is the sixth candidate reference picture.
 19. The computer progam product of claim 17, wherein the reference picture satisfies one of the following conditions: the reference picture has a second POC number closest to a third POC number of the current processing unit among reference pictures of the reference picture list; the reference picture has a smallest absolute QP difference to the current processing unit among the reference pictures; the reference picture has a same reference picture list index as a motion vector predictor, (MVP) of a current block in the current processing unit; the reference picture has a same reference picture index as the MVP; the reference picture has a largest number of MMVD blocks among the reference pictures 4; the reference picture has a smallest QP among the reference pictures; the reference picture has a lowest reference picture list index among the reference pictures; the reference picture has a lowest reference picture index among the reference pictures.
 20. The computer program product of claim 17, wherein the computer-executable instructions further cause the apparatus to obtain a default distance table for the current processing unit in the event that the reference picture is an frame. 